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b=STAaQVz2mu5IZvnat8cZ6LI37gj2LXIoSpQvDy/2iiWM8IR8VL1ULETqDO0omE7iM GVyeY27l7bUfnx9hs4eZoeGowOU08tt4TavKwDpVBk+ACSJaJL3zp8dYs3qsvGeZJd BFd1rZv9YgcXRudjbJYNxhGw632aI5erUPzrITOP5jnLuU9M/+ZSYJ3u1B6vI+UAk6 JpfOsD4Ng3IvazItvU+R72b46RmmgKde4jiRCZdPqYz5kC7Jh2fL3n7qsmUxFL9z2g 7kPwslfoOPV/smUN83Ryp7P/oxohUHHkse9teGBpD5AgxGqDtu86dCjqZXTtHD1xbG OJxpIk3ZIk8qQ== Message-ID: Date: Thu, 30 Jul 2026 15:28:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/2] mm/memory: add anonymous mTHP folios to deferred split list To: Usama Arif , Joanne Koong , akpm@linux-foundation.org, ljs@kernel.org, Johannes Weiner Cc: alex@ghiti.fr, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, willy@infradead.org, linux-mm@kvack.org References: <20260707201735.4113107-1-joannelkoong@gmail.com> <20260707201735.4113107-3-joannelkoong@gmail.com> <584098de-dd48-4004-8e7e-3d826e60c860@kernel.org> <77b3b74d-c1bb-461b-8076-8729cdcf91f5@linux.dev> <7d841b27-f60a-496f-81db-84158a0a8f8f@kernel.org> <0bdb81db-5e2f-47c9-998d-bca450644ba6@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 46ED2180003 X-Stat-Signature: 6frcxg3tz1m3k5hif3x5p63kxyn4u1ck X-Rspam-User: X-HE-Tag: 1785418095-547654 X-HE-Meta: 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 ZpSU3XNL qma0WW4Xrf4TkB1NUQs31MUz6Tb333AfUeXDmG28oyoGB/EHYagiKopG+8w4vpNDXEyWy+92+g7YxB7nDJm3fvLnxV9r8FNcvDJmw46kgpgdlVjIm6Zn6FFmmVRUrHUTMPaQhiF6Bh52ltDryFI0qn9WB6ztA8enmXVcKVGaiziIIMvSeGPHmNuRwOvQG6H/Kp3Xm/OX9dpTc6tdIkyavIqojutbNeU81VJVyYRs8biIwcDgyT5IBTT4XErpMVHp+udJxLFXUeA4844I7r9ZyPc9CGg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/29/26 15:43, Usama Arif wrote: > > > On 29/07/2026 13:36, David Hildenbrand (Arm) wrote: >> On 7/8/26 11:58, Usama Arif wrote: >>> >>> >>> >>> What if we only add the mTHPs for which the policy is set to always. >> >> That doesn't really help lock contention. And the lock contention is indeed a >> thing, as we now also want to enable the LRU cache for smaller large folios, >> which improves performance: >> >> https://lore.kernel.org/r/20260709081536.82768-1-baohua@kernel.org >> >>> >>> I think it doesn't scale if someone sets all orders to always, but if you only >>> set the 2M mTHP sysfs to always, it should be the same as what we have today >>> for PMD order? >> >> I don't see a problem with large large folios, only with small large folios :) >> >>> >>> The main motivation for this series is to try and bring the performance for >>> ARM on par with x86. One of the differences is TLB misses. I imagine the lower >>> churn in kernel by using larger page sizes will help as well. But we will >>> run into OOMs without the shrinker. >> >> Can you elaborate how this change helps here? I assume you want to enable mTHP >> in production. Which sizes? large large ones? :) >> > > One of the differences in our production between x86 and ARM hosts which we think > should perform at a similar level (but currently aren't) is TLB misses. > > On x86, we have 2M THP set to always. > On ARM, we have base page size of 64K. 2M mTHPs should help bridge the gap due to > TLB coalescing. We can't really set 2M mTHP to always as without the mTHP shrinker > we will end up with severe memory pressure and a significant increase in OOMs. > > We don't plan to enable other mTHP sizes on ARM, only 2M. > > The series by Barry is for folios above costly order, so won't impact this. > > David, Joanne, Johannes: what do you think about only adding folios that are larger > than COSTLY_ORDER to deferred split list? It's definitely better but I think it's also not an ultimate solution to the overall problem I'm afraid. As we increase COSTLY_ORDER (what people are already talking about) the behavior would change, and that's not good. -- Cheers, David