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

[Jeff Moyer]

Lukas Czerner <lczerner@xxxxxxxxxx> 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@xxxxxxxxxx>
> Reported-by: Dave Chinner <dchinner@xxxxxxxxxx>
Acked-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
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