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b=mLh2i4Pn549MOAtBAwtTl7y/1OVtrnhp4rO0PbVy/V6UmYdAI3NtxKLMphuOG7fLo wblUgc4S0AB7lxV1rH43/mDzSHF3W6Fynm7taDJXc1bX2QL4Nti6g4BSRnPmyk/DiO lNS7FaWQur6QkV/w+mv7H8Wm50v3XNiFOVIguHWqQ6oSLNB4R5+4WSZOHQkxrSuugc CMuIVKXwgrjt2zoc+cfKUOK3c473SQp01RiT5Df8tKOgu8lhdEcdUXMMrkXXCKHppD D83cximXZrxDk6WmbRv4v12unJ6ypdppHtcvqEWZQjSiy2ajbp1AztlNYQOhLWSW7u fD317OsWCcakQ== Message-ID: Date: Tue, 27 Oct 2026 11:12:41 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 11/16] mm/shmem: rescan after nonuniform folio splitting To: Zi Yan , Andrew Morton , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Johannes Weiner , Vladimir Davydov , Michal Hocko , Hugh Dickins , Baolin Wang , Lukas Czerner , Carlos Maiolino , Christian Brauner , Jan Kara , Daniel Verkamp , Jeff Xu , Muchun Song , Oscar Salvador , David Stevens , "Matthew Wilcox (Oracle)" , William Kucharski , Chris Li , Kairui Song , Nhat Pham , Miaohe Lin , Naoya Horiguchi Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20261026-fixes_shmem-v1-0-703206d5fa0c@kernel.org> <20261026-fixes_shmem-v1-11-703206d5fa0c@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: C0DD7C000D X-Stat-Signature: w11aso99z8qqzejjzhdgd1733eob6fwf X-Spam-Status: No, score=-22.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793097831-872307 X-HE-Meta: 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 zrcFEHBo gMKWOnvFCQIQoqR/Ec2msDkgz0ORCV4Wx1J1yipPNk7G8vnR3iv2S+EsWbe3sVoF0j6b4PeDSk9RyxO2V3hBiz3tZmhzSAU8wL27I4vx+LSDoLgqJC0BLTWYWfHZYcIQsjkzJ6GoCbp3jXnW4MCj3Sf2/gzZSOPmzLG8WwMBRyIZCcFpSWftnlY00ckWZb9/QzheFEaPtFrzWfWc8XZYAa3JdZQHdiZUrdYDiupdWzR0Eopu73ayTBlhDc8QtaRlxoFpDuigmADWcI9CqlVDASkR/GjbNPZVRjIthuPd/0ZlJ1uBXW7l4X/TWJ+uK0t0uckpqI9DK4a6t8bWkZa4vNqdB8RCqB6ExSTY643omdkEcBzE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/27/26 03:32, Zi Yan wrote: > On Mon Oct 26, 2026 at 5:40 AM EDT, David Hildenbrand (Arm) wrote: >> The final scan in shmem_undo_range() restarts after a successful split >> only if the original folio is no longer large. A nonuniform split can >> leave that folio large, so the scan skips the newly created folios. >> Hole punching then leaves pages within the hole allocated even though >> they could be discarded. >> >> For example, a fault below the hole can allocate a 2 MiB folio after >> boundary handling. Punching a 1 MiB hole at offset 64 KiB splits the >> folio successfully but leaves the original folio at order 4. The scan >> continues past all 512 pages, leaving 2 MiB allocated instead of 1 MiB. >> The hole reads as zero, but the pages and their block charges remain. >> > > >> Restart when the original folio is still in the mapping after partial >> truncation, identified by checking folio->mapping. If the helper >> removed the whole folio, no rescan is needed. > > This paragraph is no longer needed after Zhang Yi's truncate fix, since > truncate_inode_partial_folio() returns true only if the folio is split. > The function returns false when the whole folio is truncated[1]. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/tree/mm/truncate.c?h=mm-stable#n282 > >> >> Fixes: 7460b470a131f ("mm/truncate: use folio_split() in truncate operation") >> Cc: stable@vger.kernel.org >> Signed-off-by: David Hildenbrand (Arm) >> --- >> mm/shmem.c | 11 ++++------- >> 1 file changed, 4 insertions(+), 7 deletions(-) >> > > folio->mapping check is dropped and the comment is adjusted after the > patch is rebased on top of mm-stable because of the aforementioned > reason: > > > diff --git a/mm/shmem.c b/mm/shmem.c > index 7cf5a4d9d1ace..ddea31f44fb32 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1477,18 +1477,12 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend, > } else if (truncate_inode_partial_folio(folio, > lstart, lend, NULL, NULL)) { > /* > - * If we split a page, reset the loop so > - * that we pick up the new sub pages. > - * Otherwise the THP was entirely > - * dropped or the target range was > - * zeroed, so just continue the loop as > - * is. > + * The folio was split. Retry the scan > + * to find the split folios. > */ > - if (!folio_test_large(folio)) { > - folio_unlock(folio); > - index = start; > - break; > - } > + folio_unlock(folio); > + index = start; > + break; > } else { > /* > * Splitting failed, but the part in the > Yeah, that's straight forward. For this one I will keep Kiryl's ACK. Thanks all. -- Cheers, David