linux-kernel - Re: [PATCH v3] mm: swap: properly update readahead statistics in unuse_pte

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Date:   Fri, 17 Apr 2020 13:18:37 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrea Righi <andrea.righi@...onical.com>,
        Minchan Kim <minchan@...nel.org>,
        Anchal Agarwal <anchalag@...zon.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] mm: swap: properly update readahead statistics in unuse_pte_range()

Andrew Morton <akpm@...ux-foundation.org> writes:

> On Fri, 17 Apr 2020 11:01:22 +0800 "Huang\, Ying" <ying.huang@...el.com> wrote:
>
>> Andrea Righi <andrea.righi@...onical.com> writes:
>> 
>> > In unuse_pte_range() we blindly swap-in pages without checking if the
>> > swap entry is already present in the swap cache.
>> >
>> > By doing this, the hit/miss ratio used by the swap readahead heuristic
>> > is not properly updated and this leads to non-optimal performance during
>> > swapoff.
>> 
>> It's more important to describe why we need this patch in the patch
>> description.  So, please add some information about your use case.  And
>> please focus on the technical part instead of the business part.
>
> Confused.  I thought the changelog was quite good.  If "business part"
> means "end user effect of the patch" then that's a very important
> thing.

Previously, Andrea has described their use case in the cloud environment
to hiberate the guest and swapoff after resuming.  So swapoff
performance is important for them.  I think that should be included.
For the business part, I mean something like "Ubuntu used in AWS EC2", I
think that isn't important for the patch description.

>> Thanks!  But you don't need to do this.  You can add my Reviewed-by after
>> we have finished the work on patch description.
>
> Can you be more specific about how you want this changed?

Please use

Reviewed-by: "Huang, Ying" <ying.huang@...el.com>

Best Regards,
Huang, Ying