From: Chuck Lever III <chuck.lever@oracle.com>
To: Neil Brown <neilb@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>,
Bruce Fields <bfields@fieldses.org>,
Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
Mel Gorman <mgorman@suse.com>, Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH] SUNRPC: use congestion_wait() in svc_alloc_args()
Date: Tue, 7 Sep 2021 14:53:48 +0000 [thread overview]
Message-ID: <8ED6E493-21A6-46BC-810A-D9DA42996979@oracle.com> (raw)
In-Reply-To: <163097529362.2518.16697605173806213577@noble.neil.brown.name>
> On Sep 6, 2021, at 8:41 PM, NeilBrown <neilb@suse.de> wrote:
>
> When does a single-page GFP_KERNEL allocation fail? Ever?
>
> I know that if I add __GFP_NOFAIL then it won't fail and that is
> preferred to looping.
> I know that if I add __GFP_RETRY_MAILFAIL (or others) then it might
> fail.
> But that is the semantics for a plain GFP_KERNEL ??
>
> I recall a suggestion one that it would only fail if the process was
> being killed by the oom killer. That seems reasonable and would suggest
> that retrying is really bad. Is that true?
>
> For svc_alloc_args(), it might be better to fail and have the calling
> server thread exit. This would need to be combined with dynamic
> thread-count management so that when a request arrived, a new thread
> might be started.
I don't immediately see a benefit to killing server threads
during periods of memory exhaustion, but sometimes I lack
imagination.
> So maybe we really don't want reclaim_progress_wait(), and all current
> callers of congestion_wait() which are just waiting for allocation to
> succeed should be either change to use __GFP_NOFAIL, or to handle
> failure.
I had completely forgotten about GFP_NOFAIL. That seems like the
preferred answer, as it avoids an arbitrary time-based wait for
a memory resource. (And maybe svc_rqst_alloc() should also get
the NOFAIL treatment?).
The question in my mind is how the new alloc_pages_bulk() will
behave when passed NOFAIL. I would expect that NOFAIL would simply
guarantee that at least one page is allocated on every call.
--
Chuck Lever
next prev parent reply other threads:[~2021-09-07 14:54 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-06 4:44 [PATCH] SUNRPC: use congestion_wait() in svc_alloc_args() NeilBrown
2021-09-06 15:46 ` Chuck Lever III
2021-09-06 20:20 ` Matthew Wilcox
2021-09-06 22:13 ` Bruce Fields
2021-09-06 22:22 ` NeilBrown
2021-09-07 0:41 ` NeilBrown
2021-09-07 14:53 ` Chuck Lever III [this message]
2021-09-07 15:39 ` Bruce Fields
2021-09-07 15:41 ` Mel Gorman
2021-09-07 16:21 ` Chuck Lever III
2021-09-07 21:47 ` NeilBrown
2021-09-07 8:17 ` Mel Gorman
2021-09-06 21:52 ` NeilBrown
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