regression with poll(2)

Commit Message

Andrew Morton Aug. 21, 2012, 3:58 p.m. UTC

On Mon, 20 Aug 2012 10:02:05 -0700 Linus Torvalds <[e-mail]> wrote:

> On Mon, Aug 20, 2012 at 2:04 AM, Mel Gorman <[e-mail]> wrote:
> >
> > Can the following patch be tested please? It is reported to fix an fio
> > regression that may be similar to what you are experiencing but has not
> > been picked up yet.
> 
> Andrew, is this in your queue, or should I take this directly, or
> what? It seems to fix the problem for Eric and Sage, at least.

Yes, I have a copy queued:


From: Alex Shi <[e-mail]>
Subject: mm: correct page->pfmemalloc to fix deactivate_slab regression

cfd19c5a9ec ("mm: only set page->pfmemalloc when ALLOC_NO_WATERMARKS was
used") tried to narrow down page->pfmemalloc setting, but it missed some
places the pfmemalloc should be set.

So, in __slab_alloc, the unalignment pfmemalloc and ALLOC_NO_WATERMARKS
cause incorrect deactivate_slab() on our core2 server:

    64.73%           fio  [kernel.kallsyms]     [k] _raw_spin_lock
                     |
                     --- _raw_spin_lock
                        |
                        |---0.34%-- deactivate_slab
                        |          __slab_alloc
                        |          kmem_cache_alloc
                        |          |

That causes our fio sync write performance to have a 40% regression.

Move the checking in get_page_from_freelist() which resolves this issue.

Signed-off-by: Alex Shi <[e-mail]>
Acked-by: Mel Gorman <[e-mail]>
Cc: David Miller <[e-mail]
Cc: Peter Zijlstra <[e-mail]>
Tested-by: Eric Dumazet <[e-mail]>
Tested-by: Sage Weil <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/page_alloc.c |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

Patch

diff -puN mm/page_alloc.c~mm-correct-page-pfmemalloc-to-fix-deactivate_slab-regression mm/page_alloc.c
--- a/mm/page_alloc.c~mm-correct-page-pfmemalloc-to-fix-deactivate_slab-regression
+++ a/mm/page_alloc.c
@@ -1928,6 +1928,17 @@  this_zone_full:
 		zlc_active = 0;
 		goto zonelist_scan;
 	}
+
+	if (page)
+		/*
+		 * page->pfmemalloc is set when ALLOC_NO_WATERMARKS was
+		 * necessary to allocate the page. The expectation is
+		 * that the caller is taking steps that will free more
+		 * memory. The caller should avoid the page being used
+		 * for !PFMEMALLOC purposes.
+		 */
+		page->pfmemalloc = !!(alloc_flags & ALLOC_NO_WATERMARKS);
+
 	return page;
 }
 
@@ -2389,14 +2400,6 @@  rebalance:
 				zonelist, high_zoneidx, nodemask,
 				preferred_zone, migratetype);
 		if (page) {
-			/*
-			 * page->pfmemalloc is set when ALLOC_NO_WATERMARKS was
-			 * necessary to allocate the page. The expectation is
-			 * that the caller is taking steps that will free more
-			 * memory. The caller should avoid the page being used
-			 * for !PFMEMALLOC purposes.
-			 */
-			page->pfmemalloc = true;
 			goto got_pg;
 		}
 	}
@@ -2569,8 +2572,6 @@  retry_cpuset:
 		page = __alloc_pages_slowpath(gfp_mask, order,
 				zonelist, high_zoneidx, nodemask,
 				preferred_zone, migratetype);
-	else
-		page->pfmemalloc = false;
 
 	trace_mm_page_alloc(page, order, gfp_mask, migratetype);