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spf=pass (imf10.hostedemail.com: domain of baolin.wang@linux.alibaba.com designates 115.124.30.110 as permitted sender) smtp.mailfrom=baolin.wang@linux.alibaba.com; dmarc=pass (policy=none) header.from=linux.alibaba.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1789357258; h=from:from:sender: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:dkim-signature; bh=AoexynbmVsxSclYh9BsIybBGJ4wqU7ohzfDGpEpM46o=; b=Zey/3BGXo+IoZ1diRCAoHN9KtPZ+e0M6QAR7TAh6zmgIug4kVJRbKVlkX45n/cO9RLKYRT 3IiT79+1tAVWj8/BbPPnsth16hFIgn7Cj1pNeK9vQ/rtjjTwG2mo06S1xwUb0E+g8zuWfk 1uplskiXQ+MW4NHnaILYsWoPm4XeocI= DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1789357253; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=AoexynbmVsxSclYh9BsIybBGJ4wqU7ohzfDGpEpM46o=; b=mBEKpevleTdKUY0maLWoOm2Mi45PeaZ9jwdsjjXKVJ33NlgPosdWQb66enGhIIZsIw2QbFxnIos3B2q5OCFlHqDCe67uyuQslKJCwpkB3pEhwsjgVKapY5WM6hxmKS0uU11k7cdDKomgXmwdYMfmzhUKeunDN8KBfT9OzmFFAg0= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R301e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037033178;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=15;SR=0;TI=SMTPD_---0XAq4-4F_1789357251; Received: from 30.74.144.134(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XAq4-4F_1789357251 cluster:ay36) by smtp.aliyun-inc.com; Mon, 14 Sep 2026 11:40:52 +0800 Message-ID: <1e42ffaf-fe9d-4da0-92a4-a003f913e795@linux.alibaba.com> Date: Mon, 14 Sep 2026 11:40:50 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: shmem: ignore sysfs configs for shmem forced collapse To: Andrew Morton Cc: hughd@google.com, david@kernel.org, ziy@nvidia.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, kas@kernel.org, ljs@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <063f655b4d6c4234f3aa27ed6ecab10283ecb880.1789351825.git.baolin.wang@linux.alibaba.com> <20260913194327.019b3db96ea9b0719fc147f7@linux-foundation.org> From: Baolin Wang In-Reply-To: <20260913194327.019b3db96ea9b0719fc147f7@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 5B632C0005 X-Stat-Signature: qadr9cu8i91zn16zwjgn35mjc65meuod X-HE-Tag: 1789357255-344697 X-HE-Meta: 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 1PLNcoXf zWyTZJIxeXrJuKK2q1gCunCLJ6KIFI85OEGfkomctXcXf53gpYwhvuqaHnfcODHTwUYyeg3wqp3qiO5YSuwMOEfGLb+C4TaJdyL3FeQsacml7PuWjaHnvdilL/6UanqRs64tOgS/ZGgWFP2EA+n3C9fEpyB+SFw3WTMP3WRTqc6eKIY5k3DJHHxv8rjWGPm3MyecKbcJDa2srDh6yv4G9YfHHx+cnW+BcQxslL70WvCcsgMKXSoGuG0EikI88F0flyWtTR1MViGbUepV+baYUP/TKSuNwDJ1Ct1WlcahAlLQ+41c= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/14/26 10:43 AM, Andrew Morton wrote: > On Mon, 14 Sep 2026 10:12:41 +0800 Baolin Wang wrote: > >> According to Documentation/mm/transhuge.rst, MADV_COLLAPSE is expected to >> ignore any THP or mTHP interface settings. >> >> However, after commit 26c7d8413aaf ("mm: thp: support "THPeligible" semantics >> for mTHP with anonymous shmem"), performing MADV_COLLAPSE on shmem will >> depend on /sys/.../hugepages-2048kB/shmem_enabled being set to "inherit" >> (although that is the default), which can cause MADV_COLLAPSE to fail >> unexpectedly. > > Userspace-visible runtime regression? Yes, it could cause a userspace-visible performance regression. >> Fix this by returning the result of shmem_huge_global_enabled() directly >> when MADV_COLLAPSE is requested, allowing PMD-order collapse while ignoring >> shmem THP/mTHP settings. >> >> Fixes: 26c7d8413aaf ("mm: thp: support "THPeligible" semantics for mTHP with anonymous shmem") > > Should we backport? I'm not sure, since the issue is triggered by a rather uncommon configuration. But given that the fix is simple, I think it's fine to CC stable.