From: Mel Gorman <mgorman@techsingularity.net>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jesper Dangaard Brouer <brouer@redhat.com>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 15/28] mm, page_alloc: Move might_sleep_if check to the allocator slowpath
Date: Tue, 26 Apr 2016 17:29:28 +0100 [thread overview]
Message-ID: <20160426162928.GE2858@techsingularity.net> (raw)
In-Reply-To: <571F8645.6060503@suse.cz>
On Tue, Apr 26, 2016 at 05:16:21PM +0200, Vlastimil Babka wrote:
> On 04/26/2016 04:50 PM, Mel Gorman wrote:
> >On Tue, Apr 26, 2016 at 03:41:22PM +0200, Vlastimil Babka wrote:
> >>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.
> >>
> >
> >Either way, it struck me as odd. It does depend on the config and it's
> >marginal so if there is a problem then I can drop it.
>
> What I tried to say is that it makes sense, but it's perhaps non-obvious :)
>
> >>>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()?
> >>
> >
> >zone_reclaim has a !gfpflags_allow_blocking() check, does not call
> >cond_resched() before that check so it does not fall into an accidental
> >sleep path. I'm not seeing why the check is necessary there.
>
> Hmm I thought the primary purpose of this might_sleep_if() is to catch those
> (via the DEBUG_ATOMIC_SLEEP) that do pass __GFP_DIRECT_RECLAIM (which means
> gfpflags_allow_blocking() will be true and zone_reclaim will proceed),
It proceeds but fails immediately so what I'm failing to see is why
moving the check increases risk. I wanted to remove the check from the
path where the problem it's catching cannot happen. It does mean the
debugging check is made less frequently but it's still useful. If you
feel the safety is preferred then I'll drop the patch.
--
Mel Gorman
SUSE Labs
WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mgorman@techsingularity.net>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Jesper Dangaard Brouer <brouer@redhat.com>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 15/28] mm, page_alloc: Move might_sleep_if check to the allocator slowpath
Date: Tue, 26 Apr 2016 17:29:28 +0100 [thread overview]
Message-ID: <20160426162928.GE2858@techsingularity.net> (raw)
In-Reply-To: <571F8645.6060503@suse.cz>
On Tue, Apr 26, 2016 at 05:16:21PM +0200, Vlastimil Babka wrote:
> On 04/26/2016 04:50 PM, Mel Gorman wrote:
> >On Tue, Apr 26, 2016 at 03:41:22PM +0200, Vlastimil Babka wrote:
> >>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.
> >>
> >
> >Either way, it struck me as odd. It does depend on the config and it's
> >marginal so if there is a problem then I can drop it.
>
> What I tried to say is that it makes sense, but it's perhaps non-obvious :)
>
> >>>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()?
> >>
> >
> >zone_reclaim has a !gfpflags_allow_blocking() check, does not call
> >cond_resched() before that check so it does not fall into an accidental
> >sleep path. I'm not seeing why the check is necessary there.
>
> Hmm I thought the primary purpose of this might_sleep_if() is to catch those
> (via the DEBUG_ATOMIC_SLEEP) that do pass __GFP_DIRECT_RECLAIM (which means
> gfpflags_allow_blocking() will be true and zone_reclaim will proceed),
It proceeds but fails immediately so what I'm failing to see is why
moving the check increases risk. I wanted to remove the check from the
path where the problem it's catching cannot happen. It does mean the
debugging check is made less frequently but it's still useful. If you
feel the safety is preferred then I'll drop the patch.
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2016-04-26 16:29 UTC|newest]
Thread overview: 160+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-15 8:58 [PATCH 00/28] Optimise page alloc/free fast paths v3 Mel Gorman
2016-04-15 8:58 ` Mel Gorman
2016-04-15 8:58 ` [PATCH 01/28] mm, page_alloc: Only check PageCompound for high-order pages Mel Gorman
2016-04-15 8:58 ` Mel Gorman
2016-04-25 9:33 ` Vlastimil Babka
2016-04-25 9:33 ` Vlastimil Babka
2016-04-26 10:33 ` Mel Gorman
2016-04-26 10:33 ` Mel Gorman
2016-04-26 11:20 ` Vlastimil Babka
2016-04-26 11:20 ` Vlastimil Babka
2016-04-15 8:58 ` [PATCH 02/28] mm, page_alloc: Use new PageAnonHead helper in the free page fast path Mel Gorman
2016-04-15 8:58 ` Mel Gorman
2016-04-25 9:56 ` Vlastimil Babka
2016-04-25 9:56 ` Vlastimil Babka
2016-04-15 8:58 ` [PATCH 03/28] mm, page_alloc: Reduce branches in zone_statistics Mel Gorman
2016-04-15 8:58 ` Mel Gorman
2016-04-25 11:15 ` Vlastimil Babka
2016-04-25 11:15 ` Vlastimil Babka
2016-04-15 8:58 ` [PATCH 04/28] mm, page_alloc: Inline zone_statistics Mel Gorman
2016-04-15 8:58 ` Mel Gorman
2016-04-25 11:17 ` Vlastimil Babka
2016-04-25 11:17 ` Vlastimil Babka
2016-04-15 8:58 ` [PATCH 05/28] mm, page_alloc: Inline the fast path of the zonelist iterator Mel Gorman
2016-04-15 8:58 ` Mel Gorman
2016-04-25 14:50 ` Vlastimil Babka
2016-04-25 14:50 ` Vlastimil Babka
2016-04-26 10:30 ` Mel Gorman
2016-04-26 10:30 ` Mel Gorman
2016-04-26 11:05 ` Vlastimil Babka
2016-04-26 11:05 ` Vlastimil Babka
2016-04-15 8:58 ` [PATCH 06/28] mm, page_alloc: Use __dec_zone_state for order-0 page allocation Mel Gorman
2016-04-15 8:58 ` Mel Gorman
2016-04-26 11:25 ` Vlastimil Babka
2016-04-26 11:25 ` Vlastimil Babka
2016-04-15 8:58 ` [PATCH 07/28] mm, page_alloc: Avoid unnecessary zone lookups during pageblock operations Mel Gorman
2016-04-15 8:58 ` Mel Gorman
2016-04-26 11:29 ` Vlastimil Babka
2016-04-26 11:29 ` Vlastimil Babka
2016-04-15 8:59 ` [PATCH 08/28] mm, page_alloc: Convert alloc_flags to unsigned Mel Gorman
2016-04-15 8:59 ` Mel Gorman
2016-04-26 11:31 ` Vlastimil Babka
2016-04-26 11:31 ` Vlastimil Babka
2016-04-15 8:59 ` [PATCH 09/28] mm, page_alloc: Convert nr_fair_skipped to bool Mel Gorman
2016-04-15 8:59 ` Mel Gorman
2016-04-26 11:37 ` Vlastimil Babka
2016-04-26 11:37 ` Vlastimil Babka
2016-04-15 8:59 ` [PATCH 10/28] mm, page_alloc: Remove unnecessary local variable in get_page_from_freelist Mel Gorman
2016-04-15 8:59 ` Mel Gorman
2016-04-26 11:38 ` Vlastimil Babka
2016-04-26 11:38 ` Vlastimil Babka
2016-04-15 8:59 ` [PATCH 11/28] mm, page_alloc: Remove unnecessary initialisation " Mel Gorman
2016-04-15 8:59 ` Mel Gorman
2016-04-26 11:39 ` Vlastimil Babka
2016-04-26 11:39 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 13/28] mm, page_alloc: Remove redundant check for empty zonelist Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-15 9:07 ` [PATCH 14/28] mm, page_alloc: Simplify last cpupid reset Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 13:30 ` Vlastimil Babka
2016-04-26 13:30 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 15/28] mm, page_alloc: Move might_sleep_if check to the allocator slowpath Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 13:41 ` Vlastimil Babka
2016-04-26 13:41 ` Vlastimil Babka
2016-04-26 14:50 ` Mel Gorman
2016-04-26 14:50 ` Mel Gorman
2016-04-26 15:16 ` Vlastimil Babka
2016-04-26 15:16 ` Vlastimil Babka
2016-04-26 16:29 ` Mel Gorman [this message]
2016-04-26 16:29 ` Mel Gorman
2016-04-15 9:07 ` [PATCH 16/28] mm, page_alloc: Move __GFP_HARDWALL modifications out of the fastpath Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 14:13 ` Vlastimil Babka
2016-04-26 14:13 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 17/28] mm, page_alloc: Check once if a zone has isolated pageblocks Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 14:27 ` Vlastimil Babka
2016-04-26 14:27 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 18/28] mm, page_alloc: Shorten the page allocator fast path Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 15:23 ` Vlastimil Babka
2016-04-26 15:23 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 19/28] mm, page_alloc: Reduce cost of fair zone allocation policy retry Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 17:24 ` Vlastimil Babka
2016-04-26 17:24 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 20/28] mm, page_alloc: Shortcut watermark checks for order-0 pages Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 17:32 ` Vlastimil Babka
2016-04-26 17:32 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 21/28] mm, page_alloc: Avoid looking up the first zone in a zonelist twice Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 17:46 ` Vlastimil Babka
2016-04-26 17:46 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 22/28] mm, page_alloc: Remove field from alloc_context Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-15 9:07 ` [PATCH 23/28] mm, page_alloc: Check multiple page fields with a single branch Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 18:41 ` Vlastimil Babka
2016-04-26 18:41 ` Vlastimil Babka
2016-04-27 10:07 ` Mel Gorman
2016-04-27 10:07 ` Mel Gorman
2016-04-15 9:07 ` [PATCH 24/28] mm, page_alloc: Remove unnecessary variable from free_pcppages_bulk Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 18:43 ` Vlastimil Babka
2016-04-26 18:43 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 25/28] mm, page_alloc: Inline pageblock lookup in page free fast paths Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 19:10 ` Vlastimil Babka
2016-04-26 19:10 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 26/28] cpuset: use static key better and convert to new API Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-26 19:49 ` Vlastimil Babka
2016-04-26 19:49 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 27/28] mm, page_alloc: Defer debugging checks of freed pages until a PCP drain Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-27 11:59 ` Vlastimil Babka
2016-04-27 11:59 ` Vlastimil Babka
2016-04-27 12:01 ` [PATCH 1/3] mm, page_alloc: un-inline the bad part of free_pages_check Vlastimil Babka
2016-04-27 12:01 ` Vlastimil Babka
2016-04-27 12:01 ` [PATCH 2/3] mm, page_alloc: pull out side effects from free_pages_check Vlastimil Babka
2016-04-27 12:01 ` Vlastimil Babka
2016-04-27 12:41 ` Mel Gorman
2016-04-27 12:41 ` Mel Gorman
2016-04-27 13:00 ` Vlastimil Babka
2016-04-27 13:00 ` Vlastimil Babka
2016-04-27 12:01 ` [PATCH 3/3] mm, page_alloc: don't duplicate code in free_pcp_prepare Vlastimil Babka
2016-04-27 12:01 ` Vlastimil Babka
2016-04-27 12:37 ` [PATCH 1/3] mm, page_alloc: un-inline the bad part of free_pages_check Mel Gorman
2016-04-27 12:37 ` Mel Gorman
2016-04-27 12:53 ` Vlastimil Babka
2016-04-27 12:53 ` Vlastimil Babka
2016-04-15 9:07 ` [PATCH 28/28] mm, page_alloc: Defer debugging checks of pages allocated from the PCP Mel Gorman
2016-04-15 9:07 ` Mel Gorman
2016-04-27 14:06 ` Vlastimil Babka
2016-04-27 14:06 ` Vlastimil Babka
2016-04-27 15:31 ` Mel Gorman
2016-04-27 15:31 ` Mel Gorman
2016-05-17 6:41 ` Naoya Horiguchi
2016-05-17 6:41 ` Naoya Horiguchi
2016-05-18 7:51 ` Vlastimil Babka
2016-05-18 7:51 ` Vlastimil Babka
2016-05-18 7:55 ` Vlastimil Babka
2016-05-18 7:55 ` Vlastimil Babka
2016-05-18 8:49 ` Mel Gorman
2016-05-18 8:49 ` Mel Gorman
2016-04-26 12:04 ` [PATCH 13/28] mm, page_alloc: Remove redundant check for empty zonelist Vlastimil Babka
2016-04-26 12:04 ` Vlastimil Babka
2016-04-26 13:00 ` Mel Gorman
2016-04-26 13:00 ` Mel Gorman
2016-04-26 19:11 ` Andrew Morton
2016-04-26 19:11 ` Andrew Morton
2016-04-15 12:44 ` [PATCH 00/28] Optimise page alloc/free fast paths v3 Jesper Dangaard Brouer
2016-04-15 12:44 ` Jesper Dangaard Brouer
2016-04-15 13:08 ` Mel Gorman
2016-04-15 13:08 ` Mel Gorman
2016-04-16 7:21 ` [PATCH 12/28] mm, page_alloc: Remove unnecessary initialisation from __alloc_pages_nodemask() Mel Gorman
2016-04-16 7:21 ` Mel Gorman
2016-04-26 11:41 ` Vlastimil Babka
2016-04-26 11:41 ` Vlastimil Babka
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