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spf=pass (imf25.hostedemail.com: domain of ljs@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780584065; b=3SVtLcFBZqhwqWvjzFaqnqhtq6Y19Versf62ZS5N2TiEGsv/xSG3KozK+bigTiQ7OFt+pB 07iRMxAKQGcXEtuLxC3ac3R4KttqFdaGh+yg2VYciAniCu6wfxfRwBXzOLzyIf/rQrrGm+ LQ3coM6xsBmFkSRM3odvWneDLfjVLew= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 35C57600FC; Thu, 4 Jun 2026 14:41:05 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 813361F00893; Thu, 4 Jun 2026 14:40:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780584064; bh=CtDt3lYeen32tJjPtVhK83NQYah0kpWdJdJve8FYL6Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Ip7V26mZ3lpilTPjqq54piAcvOldqnXrk4MptULiPvlt1TPj3O9KC/WGiBCpb6sS+ FE/PcYpQMfmHU4JeXTJyoK7qBUwLxMAT46k1dxOCBZ+IVZ/92S6R53dGbiuMpcfyZK 62TXYPA9ty+/tG9g1H445TrGZInqnRDINE0QCHnsRCJNisxk2ShRvoayrgTln0h3JT Qh3k1N7Iic1u2ZWCI5CxGC92BdXhxeVP4kM4LU68/a0v9PaxSay2rbsuPPl8Q0du7s QwF1SpaHIfafTST+QIOw9/ekg10tpWZbR3mnERIgDF6duw7/NNe4JE8yOrvpGwcnGK FJin50Cz7XUIw== Date: Thu, 4 Jun 2026 15:40:49 +0100 From: Lorenzo Stoakes To: "David Hildenbrand (Arm)" Cc: Lance Yang , Nico Pache , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, liam@infradead.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com Subject: Re: [PATCH mm-unstable v18 11/14] mm/khugepaged: Introduce mTHP collapse support Message-ID: References: <20260522150009.121603-12-npache@redhat.com> <20260531071845.10875-1-lance.yang@linux.dev> <185f5699-3797-4300-8c54-bb99fc2a45e0@linux.dev> <46bb9d9e-03f0-4e26-9ac9-1cdc5ba9bf4d@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <46bb9d9e-03f0-4e26-9ac9-1cdc5ba9bf4d@kernel.org> X-HE-Tag: 1780584065-784942 X-HE-Meta: U2FsdGVkX1/evkp42QV1ZY5ML1pPutV/7B21kj1L2zN2Z5qADR+6mVY49GoG5X0XT7zWFoy32aNTIuYiJaUgmn5pFV4wettId9e9NImrsrmBtfXMwwZrUzcOFR/LSR+jV9rloOwS1bX0sk/pNKeoIP706g7zj/Fxr4R80sPvpQlNpBpLMg+GlOGwDZPMmDydu3XRBJdv0UuEgOEE5dPV/fBi+tpwnoAIzP4uf6rlvkfycIs5QRrTBqmGtjFRMt9UixCtEiOHpIRy8BirxSKcNYxlm3yk6DZngr0dhEA/rNhIX++BrK21n/pS/1jFxPY0YFVnBL1q86hm9BaDgOXaiUpWOnAOTLG5JgLyCXhuvN2uWVcS5GhpJAODc8VpZnrqQDRolcGCsDg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jun 03, 2026 at 10:05:08AM +0200, David Hildenbrand (Arm) wrote: > On 6/2/26 17:44, Lance Yang wrote: > > > > > > On 2026/6/2 18:58, Nico Pache wrote: > >> On Sun, May 31, 2026 at 1:19 AM Lance Yang wrote: > >>> > >>> > >>> [...] > >>> > >>> Hmm ... don't we lose the allocation-failure result here? > >>> > >>> Previously collapse_scan_pmd() propagated SCAN_ALLOC_HUGE_PAGE_FAIL from > >>> collapse_huge_page(), so khugepaged would call khugepaged_alloc_sleep() > >>> in khugepaged_do_scan(). > >>> > >>> Now if allocation fails and nr_collapsed stays 0, we just return > >>> SCAN_FAIL. So we won't back off via khugepaged_alloc_sleep() anymore? > >> > >> Ok I did the error propagation! I think I handled both of these cases > >> you brought up pretty easily. > > > > Thanks. > > > >> However I don't know what to do in the following case: We successfully > >> collapsed some portion of the PMD, but during that process, we also > >> hit an allocation failure. Is it best to back off entirely? or can we > >> treat some forward progress as a sign we can continue trying collapses > >> without sleeping. > >> > >> Basically, do we prioritize SCAN_ALLOC_HUGE_PAGE_FAIL or the > >> successful collapses as the returned value? > > > > Thinking out loud, forward progress should win here, the allocation > > failure only matter if we made no progress at all? > > Agreed, in the first approach, forward progress makes sense. Sounds sensible to me. > > -- > Cheers, > > David Thanks, Lorenzo