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Date: Tue, 26 Apr 2016 15:41:22 +0200 From: Vlastimil Babka <vbabka@...e.cz> To: Mel Gorman <mgorman@...hsingularity.net>, Andrew Morton <akpm@...ux-foundation.org> Cc: Jesper Dangaard Brouer <brouer@...hat.com>, Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 15/28] mm, page_alloc: Move might_sleep_if check to the allocator slowpath On 04/15/2016 11:07 AM, Mel Gorman wrote: > There is a debugging check for callers that specify __GFP_DIRECT_RECLAIM > from a context that cannot sleep. Triggering this is almost certainly > a bug but it's also overhead in the fast path. For CONFIG_DEBUG_ATOMIC_SLEEP, enabling is asking for the overhead. But for CONFIG_PREEMPT_VOLUNTARY which turns it into _cond_resched(), I guess it's not. > Move the check to the slow > path. It'll be harder to trigger as it'll only be checked when watermarks > are depleted but it'll also only be checked in a path that can sleep. Hmm what about zone_reclaim_mode=1, should the check be also duplicated to that part of get_page_from_freelist()? > Signed-off-by: Mel Gorman <mgorman@...hsingularity.net> > --- > mm/page_alloc.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 21aaef6ddd7a..9ef2f4ab9ca5 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3176,6 +3176,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > return NULL; > } > > + might_sleep_if(gfp_mask & __GFP_DIRECT_RECLAIM); > + > /* > * We also sanity check to catch abuse of atomic reserves being used by > * callers that are not in atomic context. > @@ -3369,8 +3371,6 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, > > lockdep_trace_alloc(gfp_mask); > > - might_sleep_if(gfp_mask & __GFP_DIRECT_RECLAIM); > - > if (should_fail_alloc_page(gfp_mask, order)) > return NULL; > >
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