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Message-ID: <45fc0324-4a1d-7b2c-6cbe-3755056d5981@quicinc.com>
Date:   Fri, 17 Nov 2023 11:13:20 +0530
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Subject: Re: [PATCH V3 3/3] mm: page_alloc: drain pcp lists before oom kill
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To:     Michal Hocko <mhocko@suse.com>
CC:     <akpm@linux-foundation.org>, <mgorman@techsingularity.net>,
        <david@redhat.com>, <vbabka@suse.cz>, <hannes@cmpxchg.org>,
        <quic_pkondeti@quicinc.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>
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From:   Charan Teja Kalla <quic_charante@quicinc.com>
In-Reply-To: <ZVYRJMUitykepLRy@tiehlicka>
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Thanks Michal!!

On 11/16/2023 6:25 PM, Michal Hocko wrote:
>> May be other way to look at that patch is comment is really not being
>> reflected in the code. It says, " Limit the number reserved to 1
>> pageblock or roughly 1% of a zone.", but the current code is making it 2
>> pageblocks. So, for 4M block size, it is > 1%.
>>
>> A second patch, that I will post, like not reserving the high atomic
>> page blocks on small systems -- But how to define the meaning of small
>> systems is not sure. Instead will let the system administrators chose
>> this through either:
>> a) command line param, high_atomic_reserves=off, on by default --
>> Another knob, so admins may really not like this?
>> b) CONFIG_HIGH_ATOMIC_RESERVES, which if not defined, will not reserve.
> Please don't! I do not see any admin wanting to care about this at all.
> It just takes a lot of understanding of internal MM stuff to make an
> educated guess. This should really be auto-tuned. And as responded in
> other reply my take would be to reserve a page block on if it doesn't
> consume more than 1% of memory to preserve the existing behavior yet not
> overconsume on small systems.

This idea of auto tune, by reserving a pageblock only if it doesn't
consume more than 1% of memory, seems cleaner to me.  For a page block
size of 4MB, this will turnout to be upto 400MB of RAM.

If it is fine, I can post a patch with suggested-by: you.

>