From: Vlastimil Babka <vbabka@suse.cz>
To: Michal Hocko <mhocko@suse.com>
Cc: NeilBrown <neilb@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
Theodore Ts'o <tytso@mit.edu>,
Andreas Dilger <adilger.kernel@dilger.ca>,
"Darrick J. Wong" <djwong@kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Mel Gorman <mgorman@suse.de>,
". Dave Chinner" <david@fromorbit.com>,
Jonathan Corbet <corbet@lwn.net>,
linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org
Subject: Re: [PATCH 2/6] MM: improve documentation for __GFP_NOFAIL
Date: Tue, 5 Oct 2021 14:27:45 +0200 [thread overview]
Message-ID: <eba04a07-99da-771a-ab6b-36de41f9f120@suse.cz> (raw)
In-Reply-To: <YVwyhDnE/HEnoLAi@dhcp22.suse.cz>
On 10/5/21 13:09, Michal Hocko wrote:
> On Tue 05-10-21 11:20:51, Vlastimil Babka wrote:
> [...]
>> > --- a/include/linux/gfp.h
>> > +++ b/include/linux/gfp.h
>> > @@ -209,7 +209,11 @@ struct vm_area_struct;
>> > * used only when there is no reasonable failure policy) but it is
>> > * definitely preferable to use the flag rather than opencode endless
>> > * loop around allocator.
>> > - * Using this flag for costly allocations is _highly_ discouraged.
>> > + * Use of this flag may lead to deadlocks if locks are held which would
>> > + * be needed for memory reclaim, write-back, or the timely exit of a
>> > + * process killed by the OOM-killer. Dropping any locks not absolutely
>> > + * needed is advisable before requesting a %__GFP_NOFAIL allocate.
>> > + * Using this flag for costly allocations (order>1) is _highly_ discouraged.
>>
>> We define costly as 3, not 1. But sure it's best to avoid even order>0 for
>> __GFP_NOFAIL. Advising order>1 seems arbitrary though?
>
> This is not completely arbitrary. We have a warning for any higher order
> allocation.
> rmqueue:
> WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
Oh, I missed that.
> I do agree that "Using this flag for higher order allocations is
> _highly_ discouraged.
Well, with the warning in place this is effectively forbidden, not just
discouraged.
>> > */
>> > #define __GFP_IO ((__force gfp_t)___GFP_IO)
>> > #define __GFP_FS ((__force gfp_t)___GFP_FS)
>> >
>> >
>> >
>
next prev parent reply other threads:[~2021-10-05 12:27 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-17 2:56 [PATCH 0/6 v2] congestion_wait() and GFP_NOFAIL NeilBrown
2021-09-17 2:56 ` [PATCH 6/6] XFS: remove congestion_wait() loop from xfs_buf_alloc_pages() NeilBrown
2021-09-17 2:56 ` [PATCH 5/6] XFS: remove congestion_wait() loop from kmem_alloc() NeilBrown
2021-09-17 21:45 ` Dave Chinner
2021-09-17 2:56 ` [PATCH 1/6] MM: Support __GFP_NOFAIL in alloc_pages_bulk_*() and improve doco NeilBrown
2021-09-17 14:42 ` Mel Gorman
2021-09-20 23:48 ` NeilBrown
2021-10-05 9:16 ` Vlastimil Babka
2021-09-17 2:56 ` [PATCH 3/6] EXT4: Remove ENOMEM/congestion_wait() loops NeilBrown
2021-09-17 2:56 ` [PATCH 4/6] EXT4: remove congestion_wait from ext4_bio_write_page, and simplify NeilBrown
2021-09-17 2:56 ` [PATCH 2/6] MM: improve documentation for __GFP_NOFAIL NeilBrown
2021-10-05 9:20 ` Vlastimil Babka
2021-10-05 11:09 ` Michal Hocko
2021-10-05 12:27 ` Vlastimil Babka [this message]
2021-10-06 23:14 ` Dave Chinner
2021-10-07 10:07 ` Michal Hocko
2021-10-07 23:15 ` NeilBrown
2021-10-08 7:48 ` Michal Hocko
2021-10-08 22:36 ` Dave Chinner
2021-10-11 11:57 ` Michal Hocko
2021-10-11 21:49 ` NeilBrown
2021-10-18 10:23 ` Michal Hocko
2021-10-19 4:32 ` NeilBrown
2021-10-19 13:59 ` Michal Hocko
2021-10-22 0:09 ` NeilBrown
2021-10-13 2:32 ` Dave Chinner
2021-10-13 8:26 ` Michal Hocko
2021-10-14 11:32 ` David Sterba
2021-10-14 11:46 ` Michal Hocko
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