From: Dave Chinner <david@fromorbit.com>
To: NeilBrown <neilb@suse.de>
Cc: 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.com>,
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
Subject: Re: [PATCH 5/6] XFS: remove congestion_wait() loop from kmem_alloc()
Date: Tue, 14 Sep 2021 11:31:17 +1000 [thread overview]
Message-ID: <20210914013117.GG2361455@dread.disaster.area> (raw)
In-Reply-To: <163157838439.13293.5032214643474179966.stgit@noble.brown>
On Tue, Sep 14, 2021 at 10:13:04AM +1000, NeilBrown wrote:
> Documentation commment in gfp.h discourages indefinite retry loops on
> ENOMEM and says of __GFP_NOFAIL that it
>
> is definitely preferable to use the flag rather than opencode
> endless loop around allocator.
>
> So remove the loop, instead specifying __GFP_NOFAIL if KM_MAYFAIL was
> not given.
>
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
> fs/xfs/kmem.c | 16 ++++------------
> 1 file changed, 4 insertions(+), 12 deletions(-)
>
> diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> index 6f49bf39183c..f545f3633f88 100644
> --- a/fs/xfs/kmem.c
> +++ b/fs/xfs/kmem.c
> @@ -13,19 +13,11 @@ kmem_alloc(size_t size, xfs_km_flags_t flags)
> {
> int retries = 0;
> gfp_t lflags = kmem_flags_convert(flags);
> - void *ptr;
>
> trace_kmem_alloc(size, flags, _RET_IP_);
>
> - do {
> - ptr = kmalloc(size, lflags);
> - if (ptr || (flags & KM_MAYFAIL))
> - return ptr;
> - if (!(++retries % 100))
> - xfs_err(NULL,
> - "%s(%u) possible memory allocation deadlock size %u in %s (mode:0x%x)",
> - current->comm, current->pid,
> - (unsigned int)size, __func__, lflags);
> - congestion_wait(BLK_RW_ASYNC, HZ/50);
> - } while (1);
> + if (!(flags & KM_MAYFAIL))
> + lflags |= __GFP_NOFAIL;
> +
> + return kmalloc(size, lflags);
> }
Which means we no longer get warnings about memory allocation
failing - kmem_flags_convert() sets __GFP_NOWARN for all allocations
in this loop. Hence we'll now get silent deadlocks through this code
instead of getting warnings that memory allocation is failing
repeatedly.
I also wonder about changing the backoff behaviour here (it's a 20ms
wait right now because there are not early wakeups) will affect the
behaviour, as __GFP_NOFAIL won't wait for that extra time between
allocation attempts....
And, of course, how did you test this? Sometimes we see
unpredicted behaviours as a result of "simple" changes like this
under low memory conditions...
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2021-09-14 1:31 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-14 0:13 [PATCH 0/6] congestion_wait() and GFP_NOFAIL NeilBrown
2021-09-14 0:13 ` [PATCH 2/6] MM: annotate congestion_wait() and wait_iff_congested() as ineffective NeilBrown
2021-09-15 11:56 ` Michal Hocko
2021-09-16 22:13 ` NeilBrown
2021-09-14 0:13 ` [PATCH 5/6] XFS: remove congestion_wait() loop from kmem_alloc() NeilBrown
2021-09-14 1:31 ` Dave Chinner [this message]
2021-09-14 3:27 ` NeilBrown
2021-09-14 6:05 ` Dave Chinner
2021-09-14 0:13 ` [PATCH 3/6] EXT4: Remove ENOMEM/congestion_wait() loops NeilBrown
2021-09-14 16:34 ` Mel Gorman
2021-09-14 21:48 ` NeilBrown
2021-09-15 12:06 ` Michal Hocko
2021-09-15 22:35 ` NeilBrown
2021-09-16 0:37 ` Dave Chinner
2021-09-16 6:52 ` Michal Hocko
2021-09-14 23:55 ` Dave Chinner
2021-09-15 8:59 ` Mel Gorman
2021-09-15 12:20 ` Michal Hocko
2021-09-15 14:35 ` Mel Gorman
2021-09-15 22:38 ` Dave Chinner
2021-09-16 9:00 ` Mel Gorman
2021-09-15 0:28 ` Theodore Ts'o
2021-09-15 5:25 ` NeilBrown
2021-09-15 17:02 ` Theodore Ts'o
2021-09-14 0:13 ` [PATCH 1/6] MM: improve documentation for __GFP_NOFAIL NeilBrown
2021-09-15 11:51 ` Michal Hocko
2021-09-14 0:13 ` [PATCH 6/6] XFS: remove congestion_wait() loop from xfs_buf_alloc_pages() NeilBrown
2021-09-14 2:08 ` Dave Chinner
2021-09-14 2:35 ` NeilBrown
2021-09-14 5:33 ` Dave Chinner
2021-09-14 16:45 ` Mel Gorman
2021-09-14 21:13 ` NeilBrown
2021-09-14 0:13 ` [PATCH 4/6] EXT4: remove congestion_wait from ext4_bio_write_page, and simplify NeilBrown
2021-09-17 2:56 [PATCH 0/6 v2] congestion_wait() and GFP_NOFAIL 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
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