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mm/balloon_compaction.c: don't zero ballooned pages 

Revert commit bb01b64cfa ("mm/balloon_compaction.c: enqueue zero page
to balloon device")'

Zeroing ballon pages is rather time consuming, especially when a lot of
pages are in flight. E.g. 7GB worth of ballooned memory takes 2.8s with
__GFP_ZERO while it takes ~491ms without it.

The original commit argued that zeroing will help ksmd to merge these
pages on the host but this argument is assuming that the host actually
marks balloon pages for ksm which is not universally true.  So we pay
performance penalty for something that even might not be used in the end
which is wrong.  The host can zero out pages on its own when there is a
need.

[mhocko@kernel.org: new changelog text]
Link: http://lkml.kernel.org/r/1501761557-9758-1-git-send-email-wei.w.wang@intel.com
Fixes: bb01b64cfa ("mm/balloon_compaction.c: enqueue zero page to balloon device")
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: zhenwei.pi <zhenwei.pi@youruncloud.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Wei Wang 2017-08-10 15:24:21 -07:00 committed by Linus Torvalds
parent c0a6a5ae6b
commit af54aed94b
1 changed files with 1 additions and 1 deletions
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mm/balloon_compaction.c
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@ -24,7 +24,7 @@ struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
{ {
unsigned long flags; unsigned long flags;
struct page *page = alloc_page(balloon_mapping_gfp_mask() | struct page *page = alloc_page(balloon_mapping_gfp_mask() |
__GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_ZERO); __GFP_NOMEMALLOC | __GFP_NORETRY);
if (!page) if (!page)
return NULL; return NULL;