]> git.proxmox.com Git - mirror_ubuntu-kernels.git/commit
mm, THP: don't hold mmap_sem in khugepaged when allocating THP
authorVlastimil Babka <vbabka@suse.cz>
Thu, 9 Oct 2014 22:27:00 +0000 (15:27 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 10 Oct 2014 02:25:53 +0000 (22:25 -0400)
commit8b1645685acf3c7e0b93611fb4b328ef45c47e92
tree2446890b39f06e4ddbe6101e0644fb969a790b80
parent447f05bb488bff4282088259b04f47f0f9f76760
mm, THP: don't hold mmap_sem in khugepaged when allocating THP

When allocating huge page for collapsing, khugepaged currently holds
mmap_sem for reading on the mm where collapsing occurs.  Afterwards the
read lock is dropped before write lock is taken on the same mmap_sem.

Holding mmap_sem during whole huge page allocation is therefore useless,
the vma needs to be rechecked after taking the write lock anyway.
Furthemore, huge page allocation might involve a rather long sync
compaction, and thus block any mmap_sem writers and i.e.  affect workloads
that perform frequent m(un)map or mprotect oterations.

This patch simply releases the read lock before allocating a huge page.
It also deletes an outdated comment that assumed vma must be stable, as it
was using alloc_hugepage_vma().  This is no longer true since commit
9f1b868a13ac ("mm: thp: khugepaged: add policy for finding target node").

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/huge_memory.c