linux-kernel - Re: [PATCH] mm/vmscan: fix infinite loop in drop_slab

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Message-ID: <20200908175527.GA1336071@chrisdown.name>
Date:   Tue, 8 Sep 2020 18:55:27 +0100
From:   Chris Down <chris@...isdown.name>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     zangchunxin@...edance.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH] mm/vmscan: fix infinite loop in drop_slab_node

Vlastimil Babka writes:
>On 9/8/20 5:09 PM, Chris Down wrote:
>> drop_caches by its very nature can be extremely performance intensive -- if
>> someone wants to abort after trying too long, they can just send a
>> TASK_KILLABLE signal, no? If exiting the loop and returning to usermode doesn't
>> reliably work when doing that, then _that's_ something to improve, but this
>> looks premature to me until that's demonstrated not to work.
>
>Hm there might be existings scripts (even though I dislike those) running
>drop_caches periodically, and they are currently not set up to be killed, so one
>day it might surprise someone. Dropping should be a one-time event, not a
>continual reclaim.

Sure, but these scripts can send it to their child themselves instead of using 
WCE, no? As far as I know, that's the already supported way to abort 
drop_caches-induced reclaim.