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t=1787862430; bh=1L3yxEZbWCvg5LUmRwP8ZDavWBk+Bf+rg5djBphl/1s=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=mCbG6wIrrG+wf+wFiK8+ak/XJFOgf02RCcuYCcZpXC3tCVV+oMUfKaZuB+PLZA+/Q bBqvFU/RlaUmb8rzrh233tGbgtj+5cZ0lX0cLf5Szk2Ley1p8mI+hxkXzKjsOrDc0w Qoy1yiXqTErnp5LLKhzzzEFdKekHfvujE350xJ3hULVdozTJkJOKwmJXxy2A1oe7sS g/j3UNZG2GmeAmc5QUephEnpY08momDvCUPbcEfTBieqPovU8lMhrtt0w11NopdCLg ztNGnkpYFo4vTWWTk4/hmYbyKYy05qkqR/VDmAd6iHbVWogmnkqC0QWHFftwsTlb2q 5YntX49ZLP4pA== Message-ID: <443ab5b5-2d47-4ffe-bfa2-15e47ff7469c@kernel.org> Date: Thu, 27 Aug 2026 22:26:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 20/25] s390/fbatch: no lru_add_drain_all() in s390_wiggle_split_folio() To: Claudio Imbrenda , Hugh Dickins Cc: Andrew Morton , Ackerley Tng , Alexander Viro , Baolin Wang , Barry Song , Binbin Wu , Christian Brauner , Christoph Hellwig , Christoph Lameter , JP Kobryn , Jan Kara , Jens Axboe , Johannes Weiner , Kairui Song , Kiryl Shutsemau , Lance Yang , Leonardo Bras , Lorenzo Stoakes , Marcelo Tosatti , Matthew Wilcox , Mel Gorman , Miaohe Lin , Michal Hocko , Minchan Kim , Muchun Song , Oscar Salvador , Peter Zijlstra , Qi Zheng , Rik van Riel , Sebastian Andrzej Siewior , Shakeel Butt , Suren Baghdasaryan , Vlastimil Babka , Yang Shi , Yu Zhao , Zach O'Keefe , Zi Yan , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <14a16945-529b-8bc0-ab38-3ea97e54e223@google.com> <7bf68e7b-f88c-6ca9-39ab-e9fedab0c8be@google.com> <20260826155722.0198d3ce@p-imbrenda> <2319f670-fe0b-f032-c0dc-486cbec0f3e1@google.com> <20260827145502.2fb4505b@p-imbrenda> 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-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A881A40003 X-Stat-Signature: 9w8id7szqw4it86rmcwixfaj9gtezphi X-HE-Tag: 1787862431-729431 X-HE-Meta: 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 t6n1jbrF w+BjCVNWert5bpmNcl9tLFXdmc4Z+PyCBKpeEUJII/xzvt5B27/StpFGKhkflR8JDtZffbklY97by+FksqMPqLkH7v7ci4evP3Ai9SQVxE2iB33u3tD3G/S9zKALn/a0BC5V33rAFsSDdS7vPWuzKbyhmnKFcUQJFLVLUDmJ/2t12ntgOygWwb4uUICt6mUVORo8pUXzGk9o5pwGEMWzLFTvMqSOJXiMbAFsqy6QXa8FmqR4dJ0tlJ4CShS6vdU9HHtqoH5DSRx/v1jZ9msFB7dQs55gv9Q6BrvZlSyqkZr+LDTIqS4sgBlHVi1dwWBXQ19n9f7uWeczIvfAxMd7IyI8qWyQxoSYJKifImd5KHoB4uRpHc1t7ujdaV24XtjZ++j30 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >> I most certanly don't know s390 or that code well enough to guarantee >> you that no stray references to mapped folios can remain there. What I >> can guarantee is that no references, of the kind which lru_add_drain_all() >> used to be needed to remove, can exist there: so there will no longer >> be any point in s390 (or others) calling it for that reason, to help >> split_folio() to succeed. > > we are not using it to help split_folio() succeed (although that's a > pleasant side effect). We need it even for small pages, to guarantee > that no extra reference from LRU is present on the page. Just to clarify: the LRU cache might have references (IOW a pointer) to the folio BUT the refcount of the folio is not increased. And that's what s390x cares about. [...] > >> there was an earlier time when mm did not enforce that; and Barry >> is currently looking to relax that, so the limitation intended for >> pmd-sized folios is no longer forced on the smallest large folios. >> >> If Barry's relaxation goes in before my drainage changes, then >> there is value in that s390 lru_add_drain_all() in the interim. I think we should get lru cache references sorted before we consider using them for (m)THP. If we realize that this series here cannot land any time soon, we can reconsider. -- Cheers, David