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b=EDXiZDX7+fWEtsOKVSWrY4lgWVt2eC+RjfYSDbYUa6P7A75wOtaN9iC8fFsFKDb6GgpGiMgadgvCWOPxRqE9Y7+xP259EhkKZPS6Li1C/OQq4REJ3eJMXqAR3v9Iy4BlneZK1Sl7uxHC2pT/fYmyMoOV7aaiQSXja0eH4tXpqcE= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045133197;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=14;SR=0;TI=SMTPD_---0XCTcWz3_1791554036; Received: from 30.42.72.158(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0XCTcWz3_1791554036 cluster:ay36) by smtp.aliyun-inc.com; Fri, 09 Oct 2026 21:53:57 +0800 Message-ID: <62e0ce97-1016-4f82-af38-7703c8cffefa@linux.alibaba.com> Date: Fri, 9 Oct 2026 21:53:55 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: memory: fix truncation removing mapped folios To: Pedro Falcato , "Lorenzo Stoakes (ARM)" Cc: akpm@linux-foundation.org, david@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, qi.zheng@linux.dev, jack@suse.cz, ayushr@modal.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <0d2a1809fa1cfc22ad3df26ec28b2d30e5cdf3bd.1791540483.git.baolin.wang@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: so7rq7qimtufwcf93tftgpw4iyxw5hx4 X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: C2EC020005 X-HE-Tag: 1791554044-168243 X-HE-Meta: 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 klm83prv nULYKhEsALeSJ4ZHAAhIKpZ5ozxP6AULxq4R29aFuqyPQH6bxrr8FSuO6t0okj4YBxTLsm+gq0XaYMcoxRdP6BzxMa2RLKbWZAKTDFPcA7dMC+eFPn8xrtn8/pdbPteLMq4WUs5GppzAziWVc8f5Bv5tJK3z3aJkcwNHE1TXuogd40jURzSH3xOS2xzkEFiZ9M/gWm13SiSIk0bPTTnDPT3sAzLc/ovjG5rK8qV9AcnzLsmDDYCo46HRdsl8iXhE+4oV2wxT6U3hzjtjpaVTJzC65HQNYrtEPNssMqhV1Qd8g9ndIHJgWlw0GnGd/8ug/9nmL8WaeqZaD5BRDOIEogojcKOLjjz2ROMK8mqBu7yHlljjJf9AoesqlrDGEurmNO43m0wFoc2tLTV+zuo2Vps8Q/w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/9/26 9:36 PM, Pedro Falcato wrote: > On Fri, Oct 09, 2026 at 01:00:52PM +0100, Lorenzo Stoakes (ARM) wrote: >> On Fri, Oct 09, 2026 at 06:12:03PM +0800, Baolin Wang wrote: >>> diff --git a/mm/memory.c b/mm/memory.c >>> index 1f5d5f7d39cd..0272217ad7b0 100644 >>> --- a/mm/memory.c >>> +++ b/mm/memory.c >> >>> @@ -2044,16 +2053,10 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, >>> * to ensure they are still none, thereby preventing the pte entries >>> * from being repopulated by another thread. >>> */ >>> - if (can_reclaim_pt && direct_reclaim && addr == end) >>> + if (can_reclaim_pt && direct_reclaim && addr == end) { >>> + /* rmap changes need to be observed before e.g PTEs get zapped. */ >>> + smp_wmb(); >> >> What does this pair with? You should always say what in the comment. > > Yep, this is missing a rmb to pair with. The diff I posted at > https://lore.kernel.org/linux-mm/asigKktcrSY80A_2@pedro-suse.tail5790ac.ts.net/ > had one in zap_pmd_range(), which admittedly isn't the greatest. I'm not sure if > there's a better way to do this. I don't think we need an rmb to pair with. This is because the folio_mapped() check in __filemap_remove_folio() cannot be reordered (guarded by spinlock) with the pmd_none() check in zap_pmd_range(). We just need to guarantee that when we find a pmd_none(), the removal of the folio's mapping (via tlb_flush_rmaps()) is already observed. >> rmb/wmb are generally not needed vs. acquire/release. Are you sure a wmb is >> right here? > > I don't think that works, because __folio_remove_rmap has a ton of stuff going > on, some implying full ordering, others not. Plus you'd need to switch the pmd > dereference to something like an smp_load_acquire(). Agree.