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b=FRpHjCBQXQ5Zf6i2+7aYg5ZfVma/l81fehJ3XD4KbjXDpz4wczfktm0xO4dWonVAV WtQgLSXg5sYF3D1DrcPEmrqNgxpZ+dpU4OUxVXdztvfOP52n59M3Nj6a32q4eUzq9T JSJhvYkN7CRWeSdRVaB3AlszrzlDAGfH1qIKTlMCD9AYQTNSXcj4g4QjDV6sCZzT0j /gLx5U70OUcRfv0K0vzM3FFGVC0arv3j6BPFrSSERnMQgnLnkEnyldxeBgFxjQ7Kcp HSzoqv9sPRasdUglu+TlCu3sjV1QzU3828BqMYOXYWZgblwWfCORmbBgv+CHo4hfuu c8IilCLHYED6A== Message-ID: <3a5eed44-7d4b-488c-8e04-380cd115b6dc@kernel.org> Date: Mon, 1 Jun 2026 14:06:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v18 11/14] mm/khugepaged: Introduce mTHP collapse support To: Nico Pache , Lance Yang Cc: 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, ljs@kernel.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 References: <20260522150009.121603-12-npache@redhat.com> <20260531071845.10875-1-lance.yang@linux.dev> <6a9f062c-8376-4f83-90a9-8b167f925dc6@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A4A1D180003 X-Stat-Signature: poouddmp9b6fg8dfgneseetimdi5gtsn X-HE-Tag: 1780315590-827922 X-HE-Meta: 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 m9kI2y4m 583jmIRd73IcPpsg+FoBp4I8TaK8GLMZx+bFxTFKYfQM0Ex5gg4vYfs3jKjQgX/oW4BttwJxlgACGg4aAxzkytsGQZFesVwBzVBmr1JM2jpE4aW5v+CwE3b47y+VibMOXYZh2HHe24ljsBP9WB4+D0+R6UAqRR/oimIFHajNY1dijfYo06+nIZ+C3sURkYJpUzsel8+MfSOoqxuSBb8zDcOrylhKdWLZsDgykuk9KDwbo7b6xsIL14aopKitMNV/c1NrCaIZo8gZ1y2V3NPQGa6rqK2cjbrfCNgZMzhb1WXoBWtBQjcUXb+/icg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/1/26 14:01, Nico Pache wrote: > On Sun, May 31, 2026 at 2:48 AM Lance Yang wrote: >> >> >> >> On 2026/5/31 15:18, 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? >> >> Looks like this is a more general issue with mthp_collapse() only >> returning nr_collapsed. >> >> For example, SCAN_PMD_MAPPED used to be propagated too, and >> madvise_collapse() treats that as success. With the new code, if >> nothing was collapsed by this call, that can also become SCAN_FAIL ... >> >> So I think we should keep both. > > Yeah I thought about this before, but more regarding the "incorrect" > propagation of errors; I didn't consider that those results were > actually being considered. > > I actually had a patch to track the last_failure (with some > prioritization on certain results). I think that would solve this > issue. > > Thanks for reminding me to improve this. > > Depending on how the rest of the reviews go, I can either send up a > follow up series to do some more cleanups and improvements of the > current approach or we can send out a v19. Let's do a v19. Patch #11 might need a bit of work, we can discuss offline if you want. If we could get a v19 by the end of the week, that would be nice. -- Cheers, David