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authorYang Shi <yang.shi@linux.alibaba.com>2018-10-26 15:08:50 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-10-26 16:26:35 -0700
commit85a06835f6f1ba79f0f00838ccd5ad840dd1eafb (patch)
tree91ec31587d1e465de5d5940a11f469695c7320a3 /include/linux/mm.h
parent3c0513243a4a07ebad2d59f3d972bef483818ec6 (diff)
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mm: mremap: downgrade mmap_sem to read when shrinking
Other than munmap, mremap might be used to shrink memory mapping too. So, it may hold write mmap_sem for long time when shrinking large mapping, as what commit ("mm: mmap: zap pages with read mmap_sem in munmap") described. The mremap() will not manipulate vmas anymore after __do_munmap() call for the mapping shrink use case, so it is safe to downgrade to read mmap_sem. So, the same optimization, which downgrades mmap_sem to read for zapping pages, is also feasible and reasonable to this case. The period of holding exclusive mmap_sem for shrinking large mapping would be reduced significantly with this optimization. MREMAP_FIXED and MREMAP_MAYMOVE are more complicated to adopt this optimization since they need manipulate vmas after do_munmap(), downgrading mmap_sem may create race window. Simple mapping shrink is the low hanging fruit, and it may cover the most cases of unmap with munmap together. [akpm@linux-foundation.org: tweak comment] [yang.shi@linux.alibaba.com: fix unsigned compare against 0 issue] Link: http://lkml.kernel.org/r/1538687672-17795-2-git-send-email-yang.shi@linux.alibaba.com Link: http://lkml.kernel.org/r/1538067582-60038-1-git-send-email-yang.shi@linux.alibaba.com Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Matthew Wilcox <willy@infradead.org> Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com> Cc: Colin Ian King <colin.king@canonical.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/mm.h')
-rw-r--r--include/linux/mm.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 33228a49d7d2..a023c5ce71fa 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2306,6 +2306,8 @@ extern unsigned long do_mmap(struct file *file, unsigned long addr,
unsigned long len, unsigned long prot, unsigned long flags,
vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate,
struct list_head *uf);
+extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
+ struct list_head *uf, bool downgrade);
extern int do_munmap(struct mm_struct *, unsigned long, size_t,
struct list_head *uf);