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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> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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