p71924506
/
linux_old1
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

mm, compaction: skip compound pages by order in free scanner 

The compaction free scanner is looking for PageBuddy() pages and
skipping all others.  For large compound pages such as THP or hugetlbfs,
we can save a lot of iterations if we skip them at once using their
compound_order().  This is generally unsafe and we can read a bogus
value of order due to a race, but if we are careful, the only danger is
skipping too much.

When tested with stress-highalloc from mmtests on 4GB system with 1GB
hugetlbfs pages, the vmstat compact_free_scanned count decreased by at
least 15%.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: 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>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vlastimil Babka 2015-09-08 15:02:49 -07:00 committed by Linus Torvalds
parent 29c0dde830
commit 9fcd6d2e05
1 changed files with 25 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
mm/compaction.c
View File

@ -437,6 +437,24 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
if (!valid_page)
valid_page = page;
/*
* For compound pages such as THP and hugetlbfs, we can save
* potentially a lot of iterations if we skip them at once.
* The check is racy, but we can consider only valid values
* and the only danger is skipping too much.
*/
if (PageCompound(page)) {
unsigned int comp_order = compound_order(page);
if (likely(comp_order < MAX_ORDER)) {
blockpfn += (1UL << comp_order) - 1;
cursor += (1UL << comp_order) - 1;
}
goto isolate_fail;
}
if (!PageBuddy(page))
goto isolate_fail;
@ -496,6 +514,13 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
}
/*
* There is a tiny chance that we have read bogus compound_order(),
* so be careful to not go outside of the pageblock.
*/
if (unlikely(blockpfn > end_pfn))
blockpfn = end_pfn;
trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
nr_scanned, total_isolated);