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imf08.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=dUPN8UjC; spf=pass (imf08.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.182 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780415094; b=RwuTSQS/UJoSMoWISJruifxb/9a7ZktMFMmXGeqfNanqS/Uhp2Kl+6roHwruYMQDnqraXW KKghbDR3Kq6/mNf3E0Ot34cXouKkyCxM49ssu6yr672D6XVDE2OmoldYeBJ+SuTkhTeckB xOESIwsAMJ3sc4YzcQXAQs3VNH0zwno= Message-ID: <185f5699-3797-4300-8c54-bb99fc2a45e0@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780415088; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=f8W9tKC2C6NAekt7xw/i353pEy5xESfITkwO5U4ZKyM=; b=dUPN8UjCk9D//WfVj3ZIPIfxri7y0+DyfDfey/e1A6zAzAK6UEAwk60rmDdQMBMczBTVfQ eYmfVDCyFQ4DgX5Zvih0NOTAT5JeaRkrMW9fNX91jRnKuwjIyKGOWl6TgNiUuKF1OUIs5y itnu61NoSa2Vsg4tbFTDOK/aUcpzzfM= Date: Tue, 2 Jun 2026 23:44:17 +0800 MIME-Version: 1.0 Subject: Re: [PATCH mm-unstable v18 11/14] mm/khugepaged: Introduce mTHP collapse support Content-Language: en-US To: Nico Pache 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, david@kernel.org, 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 255B3160012 X-Stat-Signature: dgr5s7wq6eqnbohp4igs8ams5fqgunr6 X-Rspam-User: X-HE-Tag: 1780415093-839794 X-HE-Meta: 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 NaB+axYy sBkxfi+pm4nsk9PegDepgcaxfUC8LXp9vNWMPsQ7DnHQjnQsp6mA2FNEL+g+Q6ugrarkfLArdEA7b7tHkHd1TBUAo+Y1vBiluWBH5L+UJBEAFYljVFCfOuyIMNcKaCazH3EESkpvtEHJjQeW3JAsRoEj1uuxrlr4oiCeH4njpR4Gq09A+HjiEUcoz3MFUMagGg/tvNGU43GZlMO2Tvehp46hFJGjTyN43nfAYM2O1sqU7Lw417TokxaxYNm5ZgBzdkXeUv9FktSu+ITdteF0rFjuaKLDRenal86odYd4NS6qSlSnzZvoh8vDUVA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/6/2 18:58, Nico Pache wrote: > On Sun, May 31, 2026 at 1:19 AM Lance Yang wrote: >> >> >> On Fri, May 22, 2026 at 09:00:06AM -0600, Nico Pache wrote: >> [...] >>> @@ -1587,10 +1749,11 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, >>> if (result == SCAN_SUCCEED) { >>> /* collapse_huge_page expects the lock to be dropped before calling */ >>> mmap_read_unlock(mm); >>> - result = collapse_huge_page(mm, start_addr, referenced, >>> - unmapped, cc, HPAGE_PMD_ORDER); >>> - /* collapse_huge_page will return with the mmap_lock released */ >>> + nr_collapsed = mthp_collapse(mm, vma, start_addr, referenced, >>> + unmapped, cc, enabled_orders); >>> + /* mmap_lock was released above, set lock_dropped */ >>> *lock_dropped = true; >>> + result = nr_collapsed ? SCAN_SUCCEED : SCAN_FAIL; >> >> 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? > This is what I currently have: > done: > if (collapsed) > return SCAN_SUCCEED; > if (alloc_failed) > return SCAN_ALLOC_HUGE_PAGE_FAIL; I'd go with this ordering :) Cheers, Lance