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| author | Yang Shi <yang.shi@linux.alibaba.com> | 2018-10-27 01:08:50 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-10-27 02:26:35 +0300 |
| commit | 85a06835f6f1ba79f0f00838ccd5ad840dd1eafb (patch) | |
| tree | 91ec31587d1e465de5d5940a11f469695c7320a3 /include/linux/mm.h | |
| parent | 3c0513243a4a07ebad2d59f3d972bef483818ec6 (diff) | |
| download | linux-85a06835f6f1ba79f0f00838ccd5ad840dd1eafb.tar.xz | |
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.h | 2 |
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); |