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From: Vlastimil Babka <vbabka@suse.cz>
To: Mel Gorman <mgorman@techsingularity.net>
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 17:16:21 +0200	[thread overview]
Message-ID: <571F8645.6060503@suse.cz> (raw)
In-Reply-To: <20160426145006.GD2858@techsingularity.net>

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), but do so 
from the wrong context. Am I getting that wrong?

  reply	other threads:[~2016-04-26 15:16 UTC|newest]

Thread overview: 80+ 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 ` [PATCH 01/28] mm, page_alloc: Only check PageCompound for high-order pages Mel Gorman
2016-04-25  9:33   ` Vlastimil Babka
2016-04-26 10:33     ` Mel Gorman
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
2016-04-25  9:56   ` Vlastimil Babka
2016-04-15  8:58 ` [PATCH 03/28] mm, page_alloc: Reduce branches in zone_statistics Mel Gorman
2016-04-25 11:15   ` Vlastimil Babka
2016-04-15  8:58 ` [PATCH 04/28] mm, page_alloc: Inline zone_statistics Mel Gorman
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
2016-04-25 14:50   ` Vlastimil Babka
2016-04-26 10:30     ` Mel Gorman
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
2016-04-26 11:25   ` Vlastimil Babka
2016-04-15  8:58 ` [PATCH 07/28] mm, page_alloc: Avoid unnecessary zone lookups during pageblock operations Mel Gorman
2016-04-26 11:29   ` Vlastimil Babka
2016-04-15  8:59 ` [PATCH 08/28] mm, page_alloc: Convert alloc_flags to unsigned Mel Gorman
2016-04-26 11:31   ` Vlastimil Babka
2016-04-15  8:59 ` [PATCH 09/28] mm, page_alloc: Convert nr_fair_skipped to bool Mel Gorman
2016-04-26 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
2016-04-26 11:38   ` Vlastimil Babka
2016-04-15  8:59 ` [PATCH 11/28] mm, page_alloc: Remove unnecessary initialisation " Mel Gorman
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   ` [PATCH 14/28] mm, page_alloc: Simplify last cpupid reset Mel Gorman
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
2016-04-26 13:41     ` Vlastimil Babka
2016-04-26 14:50       ` Mel Gorman
2016-04-26 15:16         ` Vlastimil Babka [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
2016-04-26 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
2016-04-26 14:27     ` Vlastimil Babka
2016-04-15  9:07   ` [PATCH 18/28] mm, page_alloc: Shorten the page allocator fast path Mel Gorman
2016-04-26 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
2016-04-26 17:24     ` Vlastimil Babka
2016-04-15  9:07   ` [PATCH 20/28] mm, page_alloc: Shortcut watermark checks for order-0 pages Mel Gorman
2016-04-26 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
2016-04-26 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   ` [PATCH 23/28] mm, page_alloc: Check multiple page fields with a single branch Mel Gorman
2016-04-26 18:41     ` Vlastimil Babka
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
2016-04-26 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
2016-04-26 19:10     ` Vlastimil Babka
2016-04-15  9:07   ` [PATCH 26/28] cpuset: use static key better and convert to new API Mel Gorman
2016-04-26 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
2016-04-27 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         ` [PATCH 2/3] mm, page_alloc: pull out side effects from free_pages_check Vlastimil Babka
2016-04-27 12:41           ` Mel Gorman
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 12:37         ` [PATCH 1/3] mm, page_alloc: un-inline the bad part of free_pages_check Mel Gorman
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
2016-04-27 14:06     ` Vlastimil Babka
2016-04-27 15:31       ` Mel Gorman
2016-05-17  6:41     ` Naoya Horiguchi
2016-05-18  7:51       ` Vlastimil Babka
2016-05-18  7:55         ` Vlastimil Babka
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 13:00     ` Mel Gorman
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 13:08   ` Mel Gorman
2016-04-16  7:21 ` [PATCH 12/28] mm, page_alloc: Remove unnecessary initialisation from __alloc_pages_nodemask() Mel Gorman
2016-04-26 11:41   ` Vlastimil Babka

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