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Thu, 17 Sep 2026 12:29:58 -0700 (PDT) From: Joshua Hahn To: Andrew Morton Cc: ackerleytng@google.com, Alex Shi , David Hildenbrand , Dongliang Mu , Hongxiang Lou , Johannes Weiner , Jonathan Corbet , "Liam R. Howlett" , Lorenzo Stoakes , Miaohe Lin , Michal Hocko , Mike Rapoport , Muchun Song , Nhat Pham , Oscar Salvador , Peter Xu , Randy Dunlap , Roman Gushchin , Shakeel Butt , Shuah Khan , Suren Baghdasaryan , Usama Arif , Vlastimil Babka , Wupeng Ma , Yanteng Si , Naoya Horiguchi , fvdl@google.com, jthoughton@google.com, rientjes@google.com, vannapurve@google.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH v3 0/4] Fix HugeTLB subpool used_hpages tracking Date: Thu, 17 Sep 2026 12:29:56 -0700 Message-ID: <20260917192957.3466978-1-joshua.hahnjy@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260916201307.5618114cbac4af52d98aecfa@linux-foundation.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 1394212000A X-Stat-Signature: gwqudi9kbrg3mp8iaz67nyn9g9j8ak4o X-Rspam-User: X-HE-Tag: 1789673399-196095 X-HE-Meta: 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 FumwYaxZ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 16 Sep 2026 20:13:07 -0700 Andrew Morton wrote: > On Wed, 16 Sep 2026 16:39:00 -0700 Ackerley Tng via B4 Relay wrote: > > > HugeTLB subpools currently only track used pages (used_hpages) when a > > maximum size limit (max_hpages) is configured on the mount. > > > > ... > > > > This series addresses three problem areas resulting from untracked usage > > and asymmetric error handling: > > These are rather serious-sounding problems. > > I'm seeing Fixes: for 10-year-old patches, for one last year and one > this year. The fourth patch doesn't identify what to fix. > > So if downstream people (-stable maintainers, others) follow our > recommendations, some kernels will get two of these patches, other > kernel versions will get three and some lucky kernels might get all > four. Are you confident that the patches can be split apart in this > fashion and still produce a good result? After all, we're sending > downstream some patch combinations which we didn't test. > > Also, can you speculate about why these things took so long to > discover? Hi Andrew, I'll be brave and admit that I knew there were hugetlb accounting issues for a while because I was seeing them at some ~rare~ frequency, but I couldn't figure out exactly what was happening and didn't report it. In my defense this was before LLMs were doing a good job of finding bugs in code ; -) So I'm very grateful that Ackerley took the time to find what was happening and sent the fixes. > Ho hum, complicated. Let's at least slap a Fixes: on [4/4]. My > trillion-dollar sidekick suggests a9e443086489 ("hugetlb: disable > region_add file_region coalescing"). I just reviewed the 4th part, I'm not sure if there are any userspace-visible changes for this. Maybe just an additional retry for allocating from the global subpool? > Our other little friend is talking to us: > https://sashiko.dev/#/patchset/20260916-hugetlb-subpool-always-track-used-v3-0-38aae9b5ccdd@google.com > > I'd like to queue this up promptly because it fixes things. But let's > seek additional review input and argue with Sashiko before taking that > step. Agreed, I left my reviewed tag on 2 & 3 but it seems like Sashiko is raising some concerns. Ackerley, any thoughts on those? Thank you as always, Andrew! Joshua