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authorMichal Hocko <mhocko@suse.cz>2014-10-09 15:28:52 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-10-09 22:25:59 -0400
commitaabfb57296e3dd9761e47736ec69305c95461d7d (patch)
tree379e66feb872f9f42b44b3245e52cb16ab3194bb /mm/swap_state.c
parent01c2965f0723a25209d5cf4cac630ed0f6d0edf4 (diff)
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mm: memcontrol: do not kill uncharge batching in free_pages_and_swap_cache
free_pages_and_swap_cache limits release_pages to PAGEVEC_SIZE chunks. This is not a big deal for the normal release path but it completely kills memcg uncharge batching which reduces res_counter spin_lock contention. Dave has noticed this with his page fault scalability test case on a large machine when the lock was basically dominating on all CPUs: 80.18% 80.18% [kernel] [k] _raw_spin_lock | --- _raw_spin_lock | |--66.59%-- res_counter_uncharge_until | res_counter_uncharge | uncharge_batch | uncharge_list | mem_cgroup_uncharge_list | release_pages | free_pages_and_swap_cache | tlb_flush_mmu_free | | | |--90.12%-- unmap_single_vma | | unmap_vmas | | unmap_region | | do_munmap | | vm_munmap | | sys_munmap | | system_call_fastpath | | __GI___munmap | | | --9.88%-- tlb_flush_mmu | tlb_finish_mmu | unmap_region | do_munmap | vm_munmap | sys_munmap | system_call_fastpath | __GI___munmap In his case the load was running in the root memcg and that part has been handled by reverting 05b843012335 ("mm: memcontrol: use root_mem_cgroup res_counter") because this is a clear regression, but the problem remains inside dedicated memcgs. There is no reason to limit release_pages to PAGEVEC_SIZE batches other than lru_lock held times. This logic, however, can be moved inside the function. mem_cgroup_uncharge_list and free_hot_cold_page_list do not hold any lock for the whole pages_to_free list so it is safe to call them in a single run. The release_pages() code was previously breaking the lru_lock each PAGEVEC_SIZE pages (ie, 14 pages). However this code has no usage of pagevecs so switch to breaking the lock at least every SWAP_CLUSTER_MAX (32) pages. This means that the lock acquisition frequency is approximately halved and the max hold times are approximately doubled. The now unneeded batching is removed from free_pages_and_swap_cache(). Also update the grossly out-of-date release_pages documentation. Signed-off-by: Michal Hocko <mhocko@suse.cz> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Reported-by: Dave Hansen <dave@sr71.net> Cc: Vladimir Davydov <vdavydov@parallels.com> Cc: Greg Thelen <gthelen@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap_state.c')
-rw-r--r--mm/swap_state.c14
1 files changed, 4 insertions, 10 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c
index ef1f39139b71..154444918685 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -265,18 +265,12 @@ void free_page_and_swap_cache(struct page *page)
void free_pages_and_swap_cache(struct page **pages, int nr)
{
struct page **pagep = pages;
+ int i;
lru_add_drain();
- while (nr) {
- int todo = min(nr, PAGEVEC_SIZE);
- int i;
-
- for (i = 0; i < todo; i++)
- free_swap_cache(pagep[i]);
- release_pages(pagep, todo, false);
- pagep += todo;
- nr -= todo;
- }
+ for (i = 0; i < nr; i++)
+ free_swap_cache(pagep[i]);
+ release_pages(pagep, nr, false);
}
/*