On Wed, 17 Dec 2014 16:51:21 -0800 (PST) David Rientjes <rientjes@xxxxxxxxxx> wrote:
> > > The page allocator slowpath is always called from the fastpath if the
> > > first allocation didn't succeed, so we don't know from which we allocated
> > > the page at this tracepoint.
> >
> > True, but the idea is that when we call trace_mm_page_alloc(), local
> > var `mask' holds the gfp_t which was used in the most recent allocation
> > attempt.
> >
>
> So if the fastpath succeeds, which should be the majority of the time,
> then we get a tracepoint here that says we allocated with
> __GFP_FS | __GFP_IO even though we may have PF_MEMALLOC_NOIO set. So if
> page != NULL, we can know that either the fastpath succeeded or we don't
> have PF_MEMALLOC_NOIO and were allowed to reclaim. Not sure that's very
> helpful.
>
> Easiest thing to do would be to just clear __GFP_FS and __GFP_IO when we
> clear everything not in gfp_allowed_mask, but that's pointless if the
> fastpath succeeds. I'm not sure it's worth to restructure the code with a
> possible performance overhead for the benefit of a tracepoint.
>
> And then there's the call to lockdep_trace_alloc() which does care about
> __GFP_FS. That looks broken because we need to clear __GFP_FS with
> PF_MEMALLOC_NOIO.
<head spinning>
I'm not particuarly concerned about the tracepoint and we can change
that later. The main intent here is to restore the allocation mask
when __alloc_pages_nodemask() does the "goto retry_cpuset".
(I renamed `mask' to `alloc_mask' and documented it a bit)
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: mm/page_alloc.c:__alloc_pages_nodemask(): don't alter arg gfp_mask
__alloc_pages_nodemask() strips __GFP_IO when retrying the page
allocation. But it does this by altering the function-wide variable
gfp_mask. This will cause subsequent allocation attempts to inadvertently
use the modified gfp_mask.
Also, pass the correct mask (the mask we actually used) into
trace_mm_page_alloc().
Cc: Ming Lei <ming.lei@xxxxxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff -puN mm/page_alloc.c~mm-page_allocc-__alloc_pages_nodemask-dont-alter-arg-gfp_mask mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_allocc-__alloc_pages_nodemask-dont-alter-arg-gfp_mask
+++ a/mm/page_alloc.c
@@ -2865,6 +2865,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, u
unsigned int cpuset_mems_cookie;
int alloc_flags = ALLOC_WMARK_LOW|ALLOC_CPUSET|ALLOC_FAIR;
int classzone_idx;
+ gfp_t alloc_mask; /* The gfp_t that was actually used for allocation */
gfp_mask &= gfp_allowed_mask;
@@ -2898,22 +2899,24 @@ retry_cpuset:
classzone_idx = zonelist_zone_idx(preferred_zoneref);
/* First allocation attempt */
- page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
- zonelist, high_zoneidx, alloc_flags,
- preferred_zone, classzone_idx, migratetype);
+ alloc_mask = gfp_mask|__GFP_HARDWALL;
+ page = get_page_from_freelist(alloc_mask, nodemask, order, zonelist,
+ high_zoneidx, alloc_flags, preferred_zone,
+ classzone_idx, migratetype);
if (unlikely(!page)) {
/*
* Runtime PM, block IO and its error handling path
* can deadlock because I/O on the device might not
* complete.
*/
- gfp_mask = memalloc_noio_flags(gfp_mask);
- page = __alloc_pages_slowpath(gfp_mask, order,
+ alloc_mask = memalloc_noio_flags(gfp_mask);
+
+ page = __alloc_pages_slowpath(alloc_mask, order,
zonelist, high_zoneidx, nodemask,
preferred_zone, classzone_idx, migratetype);
}
- trace_mm_page_alloc(page, order, gfp_mask, migratetype);
+ trace_mm_page_alloc(page, order, alloc_mask, migratetype);
out:
/*
_
--
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