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* mm/zsmalloc: Convert to hotplug state machineSebastian Andrzej Siewior2016-12-021-54/+13
| | | | | | | | | | | | | | | Install the callbacks via the state machine and let the core invoke the callbacks on the already online CPUs. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Cc: linux-mm@kvack.org Cc: Minchan Kim <minchan@kernel.org> Cc: rt@linutronix.de Cc: Nitin Gupta <ngupta@vflare.org> Link: http://lkml.kernel.org/r/20161126231350.10321-11-bigeasy@linutronix.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* zsmalloc: Delete an unnecessary check before the function call "iput"Markus Elfring2016-07-281-2/+1
| | | | | | | | | | | | | | iput() tests whether its argument is NULL and then returns immediately. Thus the test around the call is not needed. This issue was detected by using the Coccinelle software. Link: http://lkml.kernel.org/r/559cf499-4a01-25f9-c87f-24d906626a57@users.sourceforge.net Signed-off-by: Markus Elfring <elfring@users.sourceforge.net> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm/zsmalloc: use helper to clear page->flags bitGanesh Mahendran2016-07-281-2/+2
| | | | | | | | | | | | | Use ClearPagePrivate/ClearPagePrivate2 helpers to clear PG_private/PG_private_2 in page->flags Link: http://lkml.kernel.org/r/1467882338-4300-7-git-send-email-opensource.ganesh@gmail.com Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm/zsmalloc: add __init,__exit attributeGanesh Mahendran2016-07-281-1/+1
| | | | | | | | | | | | Add __init,__exit attribute for function that only called in module init/exit to save memory. Link: http://lkml.kernel.org/r/1467882338-4300-6-git-send-email-opensource.ganesh@gmail.com Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm/zsmalloc: keep comments consistent with codeGanesh Mahendran2016-07-281-4/+3
| | | | | | | | | | | | | | Some minor commebnt changes: 1). update zs_malloc(),zs_create_pool() function header 2). update "Usage of struct page fields" Link: http://lkml.kernel.org/r/1467882338-4300-5-git-send-email-opensource.ganesh@gmail.com Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm/zsmalloc: avoid calculate max objects of zspage twiceGanesh Mahendran2016-07-281-16/+10
| | | | | | | | | | | | | | | | | | Currently, if a class can not be merged, the max objects of zspage in that class may be calculated twice. This patch calculate max objects of zspage at the begin, and pass the value to can_merge() to decide whether the class can be merged. Also this patch remove function get_maxobj_per_zspage(), as there is no other place to call this function. Link: http://lkml.kernel.org/r/1467882338-4300-4-git-send-email-opensource.ganesh@gmail.com Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm/zsmalloc: use class->objs_per_zspage to get num of max objectsGanesh Mahendran2016-07-281-11/+7
| | | | | | | | | | | | num of max objects in zspage is stored in each size_class now. So there is no need to re-calculate it. Link: http://lkml.kernel.org/r/1467882338-4300-3-git-send-email-opensource.ganesh@gmail.com Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm/zsmalloc: take obj index back from find_alloced_objGanesh Mahendran2016-07-281-2/+6
| | | | | | | | | | | | | the obj index value should be updated after return from find_alloced_obj() to avoid CPU burning caused by unnecessary object scanning. Link: http://lkml.kernel.org/r/1467882338-4300-2-git-send-email-opensource.ganesh@gmail.com Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm/zsmalloc: use obj_index to keep consistent with othersGanesh Mahendran2016-07-281-7/+7
| | | | | | | | | | | | This is a cleanup patch. Change "index" to "obj_index" to keep consistent with others in zsmalloc. Link: http://lkml.kernel.org/r/1467882338-4300-1-git-send-email-opensource.ganesh@gmail.com Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: fix build warnings in <linux/compaction.h>Minchan Kim2016-07-261-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Randy reported below build error. > In file included from ../include/linux/balloon_compaction.h:48:0, > from ../mm/balloon_compaction.c:11: > ../include/linux/compaction.h:237:51: warning: 'struct node' declared inside parameter list [enabled by default] > static inline int compaction_register_node(struct node *node) > ../include/linux/compaction.h:237:51: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default] > ../include/linux/compaction.h:242:54: warning: 'struct node' declared inside parameter list [enabled by default] > static inline void compaction_unregister_node(struct node *node) > It was caused by non-lru page migration which needs compaction.h but compaction.h doesn't include any header to be standalone. I think proper header for non-lru page migration is migrate.h rather than compaction.h because migrate.h has already headers needed to work non-lru page migration indirectly like isolate_mode_t, migrate_mode MIGRATEPAGE_SUCCESS. [akpm@linux-foundation.org: revert mm-balloon-use-general-non-lru-movable-page-feature-fix.patch temp fix] Link: http://lkml.kernel.org/r/20160610003304.GE29779@bbox Signed-off-by: Minchan Kim <minchan@kernel.org> Reported-by: Randy Dunlap <rdunlap@infradead.org> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Gioh Kim <gi-oh.kim@profitbricks.com> Cc: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: add NR_ZSMALLOC to vmstatMinchan Kim2016-07-261-1/+6
| | | | | | | | | | | | | | | | | | | | | | | zram is very popular for some of the embedded world (e.g., TV, mobile phones). On those system, zsmalloc's consumed memory size is never trivial (one of example from real product system, total memory: 800M, zsmalloc consumed: 150M), so we have used this out of tree patch to monitor system memory behavior via /proc/vmstat. With zsmalloc in vmstat, it helps in tracking down system behavior due to memory usage. [minchan@kernel.org: zsmalloc: follow up zsmalloc vmstat] Link: http://lkml.kernel.org/r/20160607091737.GC23435@bbox [akpm@linux-foundation.org: fix build with CONFIG_ZSMALLOC=m] Link: http://lkml.kernel.org/r/1464919731-13255-1-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Cc: Sangseok Lee <sangseok.lee@lge.com> Cc: Chanho Min <chanho.min@lge.com> Cc: Chan Gyun Jeong <chan.jeong@lge.com> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: use OBJ_TAG_BIT for bit shifterMinchan Kim2016-07-261-6/+6
| | | | | | | | | | | | | Static check warns using tag as bit shifter. It doesn't break current working but not good for redability. Let's use OBJ_TAG_BIT as bit shifter instead of OBJ_ALLOCATED_TAG. Link: http://lkml.kernel.org/r/20160607045146.GF26230@bbox Signed-off-by: Minchan Kim <minchan@kernel.org> Reported-by: Dan Carpenter <dan.carpenter@oracle.com> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: page migration supportMinchan Kim2016-07-261-116/+653
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch introduces run-time migration feature for zspage. For migration, VM uses page.lru field so it would be better to not use page.next field which is unified with page.lru for own purpose. For that, firstly, we can get first object offset of the page via runtime calculation instead of using page.index so we can use page.index as link for page chaining instead of page.next. In case of huge object, it stores handle to page.index instead of next link of page chaining because huge object doesn't need to next link for page chaining. So get_next_page need to identify huge object to return NULL. For it, this patch uses PG_owner_priv_1 flag of the page flag. For migration, it supports three functions * zs_page_isolate It isolates a zspage which includes a subpage VM want to migrate from class so anyone cannot allocate new object from the zspage. We could try to isolate a zspage by the number of subpage so subsequent isolation trial of other subpage of the zpsage shouldn't fail. For that, we introduce zspage.isolated count. With that, zs_page_isolate can know whether zspage is already isolated or not for migration so if it is isolated for migration, subsequent isolation trial can be successful without trying further isolation. * zs_page_migrate First of all, it holds write-side zspage->lock to prevent migrate other subpage in zspage. Then, lock all objects in the page VM want to migrate. The reason we should lock all objects in the page is due to race between zs_map_object and zs_page_migrate. zs_map_object zs_page_migrate pin_tag(handle) obj = handle_to_obj(handle) obj_to_location(obj, &page, &obj_idx); write_lock(&zspage->lock) if (!trypin_tag(handle)) goto unpin_object zspage = get_zspage(page); read_lock(&zspage->lock); If zs_page_migrate doesn't do trypin_tag, zs_map_object's page can be stale by migration so it goes crash. If it locks all of objects successfully, it copies content from old page to new one, finally, create new zspage chain with new page. And if it's last isolated subpage in the zspage, put the zspage back to class. * zs_page_putback It returns isolated zspage to right fullness_group list if it fails to migrate a page. If it find a zspage is ZS_EMPTY, it queues zspage freeing to workqueue. See below about async zspage freeing. This patch introduces asynchronous zspage free. The reason to need it is we need page_lock to clear PG_movable but unfortunately, zs_free path should be atomic so the apporach is try to grab page_lock. If it got page_lock of all of pages successfully, it can free zspage immediately. Otherwise, it queues free request and free zspage via workqueue in process context. If zs_free finds the zspage is isolated when it try to free zspage, it delays the freeing until zs_page_putback finds it so it will free free the zspage finally. In this patch, we expand fullness_list from ZS_EMPTY to ZS_FULL. First of all, it will use ZS_EMPTY list for delay freeing. And with adding ZS_FULL list, it makes to identify whether zspage is isolated or not via list_empty(&zspage->list) test. [minchan@kernel.org: zsmalloc: keep first object offset in struct page] Link: http://lkml.kernel.org/r/1465788015-23195-1-git-send-email-minchan@kernel.org [minchan@kernel.org: zsmalloc: zspage sanity check] Link: http://lkml.kernel.org/r/20160603010129.GC3304@bbox Link: http://lkml.kernel.org/r/1464736881-24886-12-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: use freeobj for indexMinchan Kim2016-07-261-66/+73
| | | | | | | | | | | | | | Zsmalloc stores first free object's <PFN, obj_idx> position into freeobj in each zspage. If we change it with index from first_page instead of position, it makes page migration simple because we don't need to correct other entries for linked list if a page is migrated out. Link: http://lkml.kernel.org/r/1464736881-24886-11-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: separate free_zspage from putback_zspageMinchan Kim2016-07-261-16/+11
| | | | | | | | | | | | | | | Currently, putback_zspage does free zspage under class->lock if fullness become ZS_EMPTY but it makes trouble to implement locking scheme for new zspage migration. So, this patch is to separate free_zspage from putback_zspage and free zspage out of class->lock which is preparation for zspage migration. Link: http://lkml.kernel.org/r/1464736881-24886-10-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: introduce zspage structureMinchan Kim2016-07-261-289/+242
| | | | | | | | | | | | | | | | | | | | We have squeezed meta data of zspage into first page's descriptor. So, to get meta data from subpage, we should get first page first of all. But it makes trouble to implment page migration feature of zsmalloc because any place where to get first page from subpage can be raced with first page migration. IOW, first page it got could be stale. For preventing it, I have tried several approahces but it made code complicated so finally, I concluded to separate metadata from first page. Of course, it consumes more memory. IOW, 16bytes per zspage on 32bit at the moment. It means we lost 1% at *worst case*(40B/4096B) which is not bad I think at the cost of maintenance. Link: http://lkml.kernel.org/r/1464736881-24886-9-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: factor page chain functionality outMinchan Kim2016-07-261-24/+35
| | | | | | | | | | | | For page migration, we need to create page chain of zspage dynamically so this patch factors it out from alloc_zspage. Link: http://lkml.kernel.org/r/1464736881-24886-8-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: use accessorMinchan Kim2016-07-261-22/+60
| | | | | | | | | | | | Upcoming patch will change how to encode zspage meta so for easy review, this patch wraps code to access metadata as accessor. Link: http://lkml.kernel.org/r/1464736881-24886-7-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: use bit_spin_lockMinchan Kim2016-07-261-7/+3
| | | | | | | | | | | | | | Use kernel standard bit spin-lock instead of custom mess. Even, it has a bug which doesn't disable preemption. The reason we don't have any problem is that we have used it during preemption disable section by class->lock spinlock. So no need to go to stable. Link: http://lkml.kernel.org/r/1464736881-24886-6-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: keep max_object in size_classMinchan Kim2016-07-261-17/+15
| | | | | | | | | | | | Every zspage in a size_class has same number of max objects so we could move it to a size_class. Link: http://lkml.kernel.org/r/1464736881-24886-5-git-send-email-minchan@kernel.org Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* update "mm/zsmalloc: don't fail if can't create debugfs info"Dan Streetman2016-05-261-19/+16
| | | | | | | | | | | | | | | | | Some updates to commit d34f615720d1 ("mm/zsmalloc: don't fail if can't create debugfs info"): - add pr_warn to all stat failure cases - do not prevent module loading on stat failure Link: http://lkml.kernel.org/r/1463671123-5479-1-git-send-email-ddstreet@ieee.org Signed-off-by: Dan Streetman <ddstreet@ieee.org> Reviewed-by: Ganesh Mahendran <opensource.ganesh@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Dan Streetman <dan.streetman@canonical.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm/zsmalloc: don't fail if can't create debugfs infoDan Streetman2016-05-201-11/+7
| | | | | | | | | | | | | | | | | | | Change the return type of zs_pool_stat_create() to void, and remove the logic to abort pool creation if the stat debugfs dir/file could not be created. The debugfs stat file is for debugging/information only, and doesn't affect operation of zsmalloc; there is no reason to abort creating the pool if the stat file can't be created. This was seen with zswap, which used the same name for all pool creations, which caused zsmalloc to fail to create a second pool for zswap if CONFIG_ZSMALLOC_STAT was enabled. Signed-off-by: Dan Streetman <ddstreet@ieee.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Dan Streetman <dan.streetman@canonical.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: require GFP in zs_malloc()Sergey Senozhatsky2016-05-201-11/+13
| | | | | | | | | | | | | | | | | | Pass GFP flags to zs_malloc() instead of using a fixed mask supplied to zs_create_pool(), so we can be more flexible, but, more importantly, we need this to switch zram to per-cpu compression streams -- zram will try to allocate handle with preemption disabled in a fast path and switch to a slow path (using different gfp mask) if the fast one has failed. Apart from that, this also align zs_malloc() interface with zspool/zbud. [sergey.senozhatsky@gmail.com: pass GFP flags to zs_malloc() instead of using a fixed mask] Link: http://lkml.kernel.org/r/20160429150942.GA637@swordfish Link: http://lkml.kernel.org/r/20160429150942.GA637@swordfish Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: remove unused pool param in obj_freeMinchan Kim2016-05-201-4/+3
| | | | | | | | | Let's remove unused pool param in obj_free Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: reorder function parametersMinchan Kim2016-05-201-24/+26
| | | | | | | | | | Clean up function parameter ordering to order higher data structure first. Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: clean up many BUG_ONMinchan Kim2016-05-201-27/+15
| | | | | | | | | | | | | | | | | | | | | There are many BUG_ON in zsmalloc.c which is not recommened so change them as alternatives. Normal rule is as follows: 1. avoid BUG_ON if possible. Instead, use VM_BUG_ON or VM_BUG_ON_PAGE 2. use VM_BUG_ON_PAGE if we need to see struct page's fields 3. use those assertion in primitive functions so higher functions can rely on the assertion in the primitive function. 4. Don't use assertion if following instruction can trigger Oops Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: use first_page rather than pageMinchan Kim2016-05-201-30/+32
| | | | | | | | | | | Clean up function parameter "struct page". Many functions of zsmalloc expect that page paramter is "first_page" so use "first_page" rather than "page" for code readability. Signed-off-by: Minchan Kim <minchan@kernel.org> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: fix zs_can_compact() integer overflowSergey Senozhatsky2016-05-091-2/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | zs_can_compact() has two race conditions in its core calculation: unsigned long obj_wasted = zs_stat_get(class, OBJ_ALLOCATED) - zs_stat_get(class, OBJ_USED); 1) classes are not locked, so the numbers of allocated and used objects can change by the concurrent ops happening on other CPUs 2) shrinker invokes it from preemptible context Depending on the circumstances, thus, OBJ_ALLOCATED can become less than OBJ_USED, which can result in either very high or negative `total_scan' value calculated later in do_shrink_slab(). do_shrink_slab() has some logic to prevent those cases: vmscan: shrink_slab: zs_shrinker_scan+0x0/0x28 [zsmalloc] negative objects to delete nr=-62 vmscan: shrink_slab: zs_shrinker_scan+0x0/0x28 [zsmalloc] negative objects to delete nr=-62 vmscan: shrink_slab: zs_shrinker_scan+0x0/0x28 [zsmalloc] negative objects to delete nr=-64 vmscan: shrink_slab: zs_shrinker_scan+0x0/0x28 [zsmalloc] negative objects to delete nr=-62 vmscan: shrink_slab: zs_shrinker_scan+0x0/0x28 [zsmalloc] negative objects to delete nr=-62 vmscan: shrink_slab: zs_shrinker_scan+0x0/0x28 [zsmalloc] negative objects to delete nr=-62 However, due to the way `total_scan' is calculated, not every shrinker->count_objects() overflow can be spotted and handled. To demonstrate the latter, I added some debugging code to do_shrink_slab() (x86_64) and the results were: vmscan: OVERFLOW: shrinker->count_objects() == -1 [18446744073709551615] vmscan: but total_scan > 0: 92679974445502 vmscan: resulting total_scan: 92679974445502 [..] vmscan: OVERFLOW: shrinker->count_objects() == -1 [18446744073709551615] vmscan: but total_scan > 0: 22634041808232578 vmscan: resulting total_scan: 22634041808232578 Even though shrinker->count_objects() has returned an overflowed value, the resulting `total_scan' is positive, and, what is more worrisome, it is insanely huge. This value is getting used later on in shrinker->scan_objects() loop: while (total_scan >= batch_size || total_scan >= freeable) { unsigned long ret; unsigned long nr_to_scan = min(batch_size, total_scan); shrinkctl->nr_to_scan = nr_to_scan; ret = shrinker->scan_objects(shrinker, shrinkctl); if (ret == SHRINK_STOP) break; freed += ret; count_vm_events(SLABS_SCANNED, nr_to_scan); total_scan -= nr_to_scan; cond_resched(); } `total_scan >= batch_size' is true for a very-very long time and 'total_scan >= freeable' is also true for quite some time, because `freeable < 0' and `total_scan' is large enough, for example, 22634041808232578. The only break condition, in the given scheme of things, is shrinker->scan_objects() == SHRINK_STOP test, which is a bit too weak to rely on, especially in heavy zsmalloc-usage scenarios. To fix the issue, take a pool stat snapshot and use it instead of racy zs_stat_get() calls. Link: http://lkml.kernel.org/r/20160509140052.3389-1-sergey.senozhatsky@gmail.com Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Cc: <stable@vger.kernel.org> [4.3+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm/zsmalloc: add `freeable' column to pool statSergey Senozhatsky2016-03-171-7/+13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Add a new column to pool stats, which will tell how many pages ideally can be freed by class compaction, so it will be easier to analyze zsmalloc fragmentation. At the moment, we have only numbers of FULL and ALMOST_EMPTY classes, but they don't tell us how badly the class is fragmented internally. The new /sys/kernel/debug/zsmalloc/zramX/classes output look as follows: class size almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage freeable [..] 12 224 0 2 146 5 8 4 4 13 240 0 0 0 0 0 1 0 14 256 1 13 1840 1672 115 1 10 15 272 0 0 0 0 0 1 0 [..] 49 816 0 3 745 735 149 1 2 51 848 3 4 361 306 76 4 8 52 864 12 14 378 268 81 3 21 54 896 1 12 117 57 26 2 12 57 944 0 0 0 0 0 3 0 [..] Total 26 131 12709 10994 1071 134 For example, from this particular output we can easily conclude that class-896 is heavily fragmented -- it occupies 26 pages, 12 can be freed by compaction. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: drop unused member 'mapping_area->huge'YiPing Xu2016-03-171-6/+3
| | | | | | | | | | | | When unmapping a huge class page in zs_unmap_object, the page will be unmapped by kmap_atomic. the "!area->huge" branch in __zs_unmap_object is alway true, and no code set "area->huge" now, so we can drop it. Signed-off-by: YiPing Xu <xuyiping@huawei.com> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: fix migrate_zspage-zs_free race conditionJunil Lee2016-01-201-1/+13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | record_obj() in migrate_zspage() does not preserve handle's HANDLE_PIN_BIT, set by find_aloced_obj()->trypin_tag(), and implicitly (accidentally) un-pins the handle, while migrate_zspage() still performs an explicit unpin_tag() on the that handle. This additional explicit unpin_tag() introduces a race condition with zs_free(), which can pin that handle by this time, so the handle becomes un-pinned. Schematically, it goes like this: CPU0 CPU1 migrate_zspage find_alloced_obj trypin_tag set HANDLE_PIN_BIT zs_free() pin_tag() obj_malloc() -- new object, no tag record_obj() -- remove HANDLE_PIN_BIT set HANDLE_PIN_BIT unpin_tag() -- remove zs_free's HANDLE_PIN_BIT The race condition may result in a NULL pointer dereference: Unable to handle kernel NULL pointer dereference at virtual address 00000000 CPU: 0 PID: 19001 Comm: CookieMonsterCl Tainted: PC is at get_zspage_mapping+0x0/0x24 LR is at obj_free.isra.22+0x64/0x128 Call trace: get_zspage_mapping+0x0/0x24 zs_free+0x88/0x114 zram_free_page+0x64/0xcc zram_slot_free_notify+0x90/0x108 swap_entry_free+0x278/0x294 free_swap_and_cache+0x38/0x11c unmap_single_vma+0x480/0x5c8 unmap_vmas+0x44/0x60 exit_mmap+0x50/0x110 mmput+0x58/0xe0 do_exit+0x320/0x8dc do_group_exit+0x44/0xa8 get_signal+0x538/0x580 do_signal+0x98/0x4b8 do_notify_resume+0x14/0x5c This patch keeps the lock bit in migration path and update value atomically. Signed-off-by: Junil Lee <junil0814.lee@lge.com> Signed-off-by: Minchan Kim <minchan@kernel.org> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Cc: <stable@vger.kernel.org> [4.1+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: reorganize struct size_class to pack 4 bytes holeWeijie Yang2016-01-151-2/+2
| | | | | | | | | | | Reoder the pages_per_zspage field in struct size_class which can eliminate the 4 bytes hole between it and stats field. Signed-off-by: Weijie Yang <weijie.yang@samsung.com> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: use page->private instead of page->first_pageKirill A. Shutemov2015-11-061-6/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | We are going to rework how compound_head() work. It will not use page->first_page as we have it now. The only other user of page->first_page beyond compound pages is zsmalloc. Let's use page->private instead of page->first_page here. It occupies the same storage space. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Cc: Christoph Lameter <cl@linux.com> Cc: David Rientjes <rientjes@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: reduce size_class memory usageSergey Senozhatsky2015-11-061-4/+13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Each `struct size_class' contains `struct zs_size_stat': an array of NR_ZS_STAT_TYPE `unsigned long'. For zsmalloc built with no CONFIG_ZSMALLOC_STAT this results in a waste of `2 * sizeof(unsigned long)' per-class. The patch removes unneeded `struct zs_size_stat' members by redefining NR_ZS_STAT_TYPE (max stat idx in array). Since both NR_ZS_STAT_TYPE and zs_stat_type are compile time constants, GCC can eliminate zs_stat_inc()/zs_stat_dec() calls that use zs_stat_type larger than NR_ZS_STAT_TYPE: CLASS_ALMOST_EMPTY and CLASS_ALMOST_FULL at the moment. ./scripts/bloat-o-meter mm/zsmalloc.o.old mm/zsmalloc.o.new add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-39 (-39) function old new delta fix_fullness_group 97 94 -3 insert_zspage 100 86 -14 remove_zspage 141 119 -22 To summarize: a) each class now uses less memory b) we avoid a number of dec/inc stats (a minor optimization, but still). The gain will increase once we introduce additional stats. A simple IO test. iozone -t 4 -R -r 32K -s 60M -I +Z patched base " Initial write " 4145599.06 4127509.75 " Rewrite " 4146225.94 4223618.50 " Read " 17157606.00 17211329.50 " Re-read " 17380428.00 17267650.50 " Reverse Read " 16742768.00 16162732.75 " Stride read " 16586245.75 16073934.25 " Random read " 16349587.50 15799401.75 " Mixed workload " 10344230.62 9775551.50 " Random write " 4277700.62 4260019.69 " Pwrite " 4302049.12 4313703.88 " Pread " 6164463.16 6126536.72 " Fwrite " 7131195.00 6952586.00 " Fread " 12682602.25 12619207.50 Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm/zsmalloc.c: remove useless line in obj_free()Hui Zhu2015-11-061-3/+0
| | | | | | | | Signed-off-by: Hui Zhu <zhuhui@xiaomi.com> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: don't test shrinker_enabled in zs_shrinker_count()Sergey Senozhatsky2015-11-061-3/+0
| | | | | | | | | | | We don't let user to disable shrinker in zsmalloc (once it's been enabled), so no need to check ->shrinker_enabled in zs_shrinker_count(), at the moment at least. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: use preempt.h for in_interrupt()Sergey Senozhatsky2015-11-061-1/+1
| | | | | | | | | | | | | | A cosmetic change. Commit c60369f01125 ("staging: zsmalloc: prevent mappping in interrupt context") added in_interrupt() check to zs_map_object() and 'hardirq.h' include; but in_interrupt() macro is defined in 'preempt.h' not in 'hardirq.h', so include it instead. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: fix obj_to_head use page_private(page) as value but not pointerHui Zhu2015-11-061-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | In obj_malloc(): if (!class->huge) /* record handle in the header of allocated chunk */ link->handle = handle; else /* record handle in first_page->private */ set_page_private(first_page, handle); In the hugepage we save handle to private directly. But in obj_to_head(): if (class->huge) { VM_BUG_ON(!is_first_page(page)); return *(unsigned long *)page_private(page); } else return *(unsigned long *)obj; It is used as a pointer. The reason why there is no problem until now is huge-class page is born with ZS_FULL so it can't be migrated. However, we need this patch for future work: "VM-aware zsmalloced page migration" to reduce external fragmentation. Signed-off-by: Hui Zhu <zhuhui@xiaomi.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: add comments for ->inuse to zspageHui Zhu2015-11-061-0/+1
| | | | | | | | | | [akpm@linux-foundation.org: fix grammar] Signed-off-by: Hui Zhu <zhuhui@xiaomi.com> Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Dan Streetman <ddstreet@ieee.org> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: zsmalloc: constify struct zs_pool nameSergey SENOZHATSKY2015-11-061-5/+5
| | | | | | | | | | | Constify `struct zs_pool' ->name. [akpm@inux-foundation.org: constify zpool_create_pool()'s `type' arg also] Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Dan Streetman <ddstreet@ieee.org> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* mm: zpool: constify the zpool_opsKrzysztof Kozlowski2015-09-081-1/+2
| | | | | | | | | | The structure zpool_ops is not modified so make the pointer to it a pointer to const. Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com> Acked-by: Dan Streetman <ddstreet@ieee.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: remove null check from destroy_handle_cache()Sergey Senozhatsky2015-09-081-2/+1
| | | | | | | | | | | We can pass a NULL cache pointer to kmem_cache_destroy(), because it NULL-checks its argument now. Remove redundant test from destroy_handle_cache(). Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: do not take class lock in zs_shrinker_count()Sergey Senozhatsky2015-09-081-4/+0
| | | | | | | | | | | | | | | | | | | | | We can avoid taking class ->lock around zs_can_compact() in zs_shrinker_count(), because the number that we return back is outdated in general case, by design. We have different sources that are able to change class's state right after we return from zs_can_compact() -- ongoing I/O operations, manually triggered compaction, or two of them happening simultaneously. We re-do this calculations during compaction on a per class basis anyway. zs_unregister_shrinker() will not return until we have an active shrinker, so classes won't unexpectedly disappear while zs_shrinker_count() iterates them. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: use class->pages_per_zspageMinchan Kim2015-09-081-3/+2
| | | | | | | | | | There is no need to recalcurate pages_per_zspage in runtime. Just use class->pages_per_zspage to avoid unnecessary runtime overhead. Signed-off-by: Minchan Kim <minchan@kernel.org> Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: consider ZS_ALMOST_FULL as migrate sourceMinchan Kim2015-09-081-7/+10
| | | | | | | | | | | | There is no reason to prevent select ZS_ALMOST_FULL as migration source if we cannot find source from ZS_ALMOST_EMPTY. With this patch, zs_can_compact will return more exact result. Signed-off-by: Minchan Kim <minchan.kim@lge.com> Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: partial page ordering within a fullness_listSergey Senozhatsky2015-09-081-5/+14
| | | | | | | | | | | | | | | | | | | | | We want to see more ZS_FULL pages and less ZS_ALMOST_{FULL, EMPTY} pages. Put a page with higher ->inuse count first within its ->fullness_list, which will give us better chances to fill up this page with new objects (find_get_zspage() return ->fullness_list head for new object allocation), so some zspages will become ZS_ALMOST_FULL/ZS_FULL quicker. It performs a trivial and cheap ->inuse compare which does not slow down zsmalloc and in the worst case keeps the list pages in no particular order. A more expensive solution could sort fullness_list by ->inuse count. [minchan@kernel.org: code adjustments] Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: use shrinker to trigger auto-compactionSergey Senozhatsky2015-09-081-0/+78
| | | | | | | | | | | | | | | | | | | | | | | | | | | | Perform automatic pool compaction by a shrinker when system is getting tight on memory. User-space has a very little knowledge regarding zsmalloc fragmentation and basically has no mechanism to tell whether compaction will result in any memory gain. Another issue is that user space is not always aware of the fact that system is getting tight on memory. Which leads to very uncomfortable scenarios when user space may start issuing compaction 'randomly' or from crontab (for example). Fragmentation is not always necessarily bad, allocated and unused objects, after all, may be filled with the data later, w/o the need of allocating a new zspage. On the other hand, we obviously don't want to waste memory when the system needs it. Compaction now has a relatively quick pool scan so we are able to estimate the number of pages that will be freed easily, which makes it possible to call this function from a shrinker->count_objects() callback. We also abort compaction as soon as we detect that we can't free any pages any more, preventing wasteful objects migrations. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Suggested-by: Minchan Kim <minchan@kernel.org> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: account the number of compacted pagesSergey Senozhatsky2015-09-081-10/+17
| | | | | | | | | | | | | | | | | | | | | Compaction returns back to zram the number of migrated objects, which is quite uninformative -- we have objects of different sizes so user space cannot obtain any valuable data from that number. Change compaction to operate in terms of pages and return back to compaction issuer the number of pages that were freed during compaction. So from now on we will export more meaningful value in zram<id>/mm_stat -- the number of freed (compacted) pages. This requires: (a) a rename of `num_migrated' to 'pages_compacted' (b) a internal API change -- return first_page's fullness_group from putback_zspage(), so we know when putback_zspage() did free_zspage(). It helps us to account compaction stats correctly. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc/zram: introduce zs_pool_stats apiSergey Senozhatsky2015-09-081-14/+15
| | | | | | | | | | | | | | | | | | | | | | | | `zs_compact_control' accounts the number of migrated objects but it has a limited lifespan -- we lose it as soon as zs_compaction() returns back to zram. It worked fine, because (a) zram had it's own counter of migrated objects and (b) only zram could trigger compaction. However, this does not work for automatic pool compaction (not issued by zram). To account objects migrated during auto-compaction (issued by the shrinker) we need to store this number in zs_pool. Define a new `struct zs_pool_stats' structure to keep zs_pool's stats there. It provides only `num_migrated', as of this writing, but it surely can be extended. A new zsmalloc zs_pool_stats() symbol exports zs_pool's stats back to caller. Use zs_pool_stats() in zram and remove `num_migrated' from zram_stats. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Suggested-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* zsmalloc: cosmetic compaction code adjustmentsSergey Senozhatsky2015-09-081-6/+6
| | | | | | | | | | | | | | | | | Change zs_object_copy() argument order to be (DST, SRC) rather than (SRC, DST). copy/move functions usually have (to, from) arguments order. Rename alloc_target_page() to isolate_target_page(). This function doesn't allocate anything, it isolates target page, pretty much like isolate_source_page(). Tweak __zs_compact() comment. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Acked-by: Minchan Kim <minchan@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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