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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 00721157ae682-85e5ed1cd5bsm3672297b3.17.2026.08.28.01.57.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Aug 2026 01:57:30 -0700 (PDT) Date: Fri, 28 Aug 2026 01:57:25 -0700 (PDT) From: Hugh Dickins To: Claudio Imbrenda cc: Hugh Dickins , Andrew Morton , Ackerley Tng , Alexander Viro , Baolin Wang , Barry Song , Binbin Wu , Christian Brauner , Christoph Hellwig , Christoph Lameter , David Hildenbrand , 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 Subject: Re: [PATCH 20/25] s390/fbatch: no lru_add_drain_all() in s390_wiggle_split_folio() In-Reply-To: <20260827145502.2fb4505b@p-imbrenda> Message-ID: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 24DA3120004 X-Stat-Signature: eu1a67xdyhshee97r76atzcnotg8kwmq X-HE-Tag: 1787907452-912054 X-HE-Meta: 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 r8iGv6tD 1wjUGE3pmN6OaAHKw4m0uKbi+8h8dBmXy1mvAdEDCQZBnRD3ioxG/s4RfuGz15Jd2NjrCf/pxkwDwuycG71EeY3kF/e3QzE0OhVJwICLMDPrBxPSkXegPQwp8QKiHm1AX0mhgiA17rpwdSWzDtiwSdJbaat2UTvjGBXC5zo8FM4LC2x1yQL1ed7nD2nAXHEEIMMS52NPNv+N+u+CO3p7F5X+YqnSXTu8QSqInnKJDTOX+eGg73D5NSU4ppInCnbHCvVDh/YXmuG4zXqJ/j9SA8KOW8C8BYseUZzPduaFgcRuKywoY9yvMwTUZ5prGzFm5mF3cdAdfP6ppBmHLFg6QK5/TqYB8ts13hWqslo2SUizAyqPNJ2tnPwjwxt7dkg34WBjTgOlcAaRWAfrGk+y2xCjh1tZMvP8JJ9i5fb3x0iUVit+RpTGzKNokguTBR9ke0RMN412vjmkUjnk08h+f7GLSH889FnavLOQZ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 27 Aug 2026, Claudio Imbrenda wrote: > On Thu, 27 Aug 2026 01:49:12 -0700 (PDT) > Hugh Dickins wrote: ... > > > > 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. Ah, thanks for explaining, that all makes more sense to me now. I remember from when working on memfd write sealing years ago, it too had to be able to account for every page reference before proceeding, and resorted to lru_add_drain() and lru_add_drain_all() to help - those now removed in 14/25 of this series. ... > > If Barry's relaxation goes in before my drainage changes, then > > there is value in that s390 lru_add_drain_all() in the interim. > > hmmm so, should it stay for now, then? The s390 lru_add_drain_all() should go whenever the rest of this series goes in. It's not essential for the callers to be removed immediately, no correctness requirement; but nicer if we can get rid of most of them. I'm hoping this patch can just go in along with the rest via the mm tree - and I'm sure you can trust David Hildenbrand to understand and protect s390's interests. > > also: I'm working on completely reworking how the transition from > non-secure to secure is handled, with the explicit goal of getting rid > of that kludge we are currently using. That will also get rid of the > lru drain. But it will take some time (I hope to have something by the > end of the year) Good luck! Hugh