linux-kernel - Re: [PATCH 1/2] xen/blkback: turn the cache purge LRU interval into a parameter

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Date:   Thu, 15 Oct 2020 17:08:49 +0200
From:   SeongJae Park <sjpark@...zon.com>
To:     Roger Pau Monne <roger.pau@...rix.com>
CC:     <linux-kernel@...r.kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jens Axboe <axboe@...nel.dk>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        SeongJae Park <sjpark@...zon.de>,
        <xen-devel@...ts.xenproject.org>, <linux-block@...r.kernel.org>,
        "J . Roeleveld" <joost@...arean.org>,
        Jürgen Groß <jgross@...e.com>
Subject: Re: [PATCH 1/2] xen/blkback: turn the cache purge LRU interval into a parameter

On Thu, 15 Oct 2020 16:24:15 +0200 Roger Pau Monne <roger.pau@...rix.com> wrote:

> Assume that reads and writes to the variable will be atomic. The worse
> that could happen is that one of the LRU intervals is not calculated
> properly if a partially written value is read, but that would only be
> a transient issue.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
> ---
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: SeongJae Park <sjpark@...zon.de>
> Cc: xen-devel@...ts.xenproject.org
> Cc: linux-block@...r.kernel.org
> Cc: J. Roeleveld <joost@...arean.org>
> Cc: Jürgen Groß <jgross@...e.com>
> ---
>  Documentation/ABI/testing/sysfs-driver-xen-blkback | 10 ++++++++++
>  drivers/block/xen-blkback/blkback.c                |  9 ++++++---
>  2 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback
> index ecb7942ff146..776f25d335ca 100644
> --- a/Documentation/ABI/testing/sysfs-driver-xen-blkback
> +++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback
> @@ -35,3 +35,13 @@ Description:
>                  controls the duration in milliseconds that blkback will not
>                  cache any page not backed by a grant mapping.
>                  The default is 10ms.
> +
> +What:           /sys/module/xen_blkback/parameters/lru_internval
> +Date:           October 2020
> +KernelVersion:  5.10
> +Contact:        Roger Pau Monné <roger.pau@...rix.com>
> +Description:
> +                The LRU mechanism to clean the lists of persistent grants needs
> +                to be executed periodically. This parameter controls the time
> +                interval between consecutive executions of the purge mechanism
> +                is set in ms.

I think noticing the default value (100ms) here would be better.


Thanks,
SeongJae Park