linux-kernel - Re: [PATCH 2/2 v5] loop: Limit the number of requests in the bio list

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Message-ID: <x49haobdlta.fsf@segfault.boston.devel.redhat.com>
Date:	Tue, 27 Nov 2012 11:58:57 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	axboe@...nel.dk, akpm@...ux-foundation.org
Subject: Re: [PATCH 2/2 v5] loop: Limit the number of requests in the bio list

Lukas Czerner <lczerner@...hat.com> writes:

> Currently there is not limitation of number of requests in the loop bio
> list. This can lead into some nasty situations when the caller spawns
> tons of bio requests taking huge amount of memory. This is even more
> obvious with discard where blkdev_issue_discard() will submit all bios
> for the range and wait for them to finish afterwards. On really big loop
> devices and slow backing file system this can lead to OOM situation as
> reported by Dave Chinner.
>
> With this patch we will wait in loop_make_request() if the number of
> bios in the loop bio list would exceed 'nr_congestion_on'.
> We'll wake up the process as we process the bios form the list. Some
> threshold hysteresis is in place to avoid high frequency oscillation.
>
> Signed-off-by: Lukas Czerner <lczerner@...hat.com>
> Reported-by: Dave Chinner <dchinner@...hat.com>
Acked-by: Jeff Moyer <jmoyer@...hat.com>
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