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Re: [Xen-devel] [PATCH v2 0/1] xen/blkback: Aggressively shrink page pools if a memory pressure is detected

On 05.12.19 16:09, SeongJae Park wrote:
> Each `blkif` has a free pages pool for the grant mapping.  The size of
> the pool starts from zero and be increased on demand while processing
> the I/O requests.  If current I/O requests handling is finished or 100
> milliseconds has passed since last I/O requests handling, it checks and
> shrinks the pool to not exceed the size limit, `max_buffer_pages`.
> Therefore, `blkfront` running guests can cause a memory pressure in the
> `blkback` running guest by attaching a large number of block devices and
> inducing I/O.  System administrators can avoid such problematic
> situations by limiting the maximum number of devices each guest can
> attach.  However, finding the optimal limit is not so easy.  Improper
> set of the limit can result in the memory pressure or a resource
> underutilization.  This commit avoids such problematic situations by
> shrinking the pools aggressively (further the limit) for a while (users
> can set this duration via a module parameter) if a memory pressure is
> detected.
> Base Version
> ------------
> This patch is based on v5.4.  A complete tree is also available at my
> public git repo:
> https://github.com/sjp38/linux/tree/blkback_aggressive_shrinking_v2
> Patch History
> -------------
> Changes from v1 
> (https://lore.kernel.org/xen-devel/20191204113419.2298-1-sjpark@xxxxxxxxxx/)
>  - Adjust the description to not use the term, `arbitrarily` (suggested
>    by Paul Durrant)
>  - Specify time unit of the duration in the parameter description,
>    (suggested by Maximilian Heyne)
>  - Change default aggressive shrinking duration from 1ms to 10ms
>  - Merged two patches into one single patch
> SeongJae Park (1):
>   xen/blkback: Aggressively shrink page pools if a memory pressure is
>     detected
>  drivers/block/xen-blkback/blkback.c | 35 +++++++++++++++++++++++++++--
>  1 file changed, 33 insertions(+), 2 deletions(-)

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SeongJae Park


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