Re: regression with poll(2)

On Mon, 20 Aug 2012 10:02:05 -0700 Linus Torvalds [off-list ref] wrote:

On Mon, Aug 20, 2012 at 2:04 AM, Mel Gorman [off-list ref] wrote:

quoted

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 <redacted>
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 <redacted>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: David Miller <davem@davemloft.net
Cc: Peter Zijlstra <redacted>
Tested-by: Eric Dumazet <redacted>
Tested-by: Sage Weil <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

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);
 

_