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Date:   Fri, 24 Nov 2023 11:24:28 -0800 (PST)
From:   David Rientjes <rientjes@google.com>
To:     Charan Teja Kalla <quic_charante@quicinc.com>
cc:     akpm@linux-foundation.org, mgorman@techsingularity.net,
        mhocko@suse.com, david@redhat.com, vbabka@suse.cz,
        hannes@cmpxchg.org, quic_pkondeti@quicinc.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH V3 2/2] mm: page_alloc: enforce minimum zone size to do
 high atomic reserves
In-Reply-To: <c3a2a48e2cfe08176a80eaf01c110deb9e918055.1700821416.git.quic_charante@quicinc.com>
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References: <cover.1700821416.git.quic_charante@quicinc.com> <c3a2a48e2cfe08176a80eaf01c110deb9e918055.1700821416.git.quic_charante@quicinc.com>
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On Fri, 24 Nov 2023, Charan Teja Kalla wrote:

> Highatomic reserves are set to roughly 1% of zone for maximum and a
> pageblock size for minimum.  Encountered a system with the below
> configuration:
> Normal free:7728kB boost:0kB min:804kB low:1004kB high:1204kB
> reserved_highatomic:8192KB managed:49224kB
> 
> On such systems, even a single pageblock makes highatomic reserves are
> set to ~8% of the zone memory. This high value can easily exert pressure
> on the zone.
> 
> Per discussion with Michal and Mel, it is not much useful to reserve
> the memory for highatomic allocations on such small systems[1]. Since
> the minimum size for high atomic reserves is always going to be a
> pageblock size and if 1% of zone managed pages is going to be below
> pageblock size, don't reserve memory for high atomic allocations. Thanks
> Michal for this suggestion[2].
> 
> Since no memory is being reserved for high atomic allocations and if
> respective allocation failures are seen, this patch can be reverted.
> 
> [1] https://lore.kernel.org/linux-mm/20231117161956.d3yjdxhhm4rhl7h2@techsingularity.net/
> [2] https://lore.kernel.org/linux-mm/ZVYRJMUitykepLRy@tiehlicka/
> 
> Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>

Acked-by: David Rientjes <rientjes@google.com>