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 Yq2nZxVT ltfmBXWtgPdjlmM7NG7Xte8v+qFmOpuoI76dm5SkF2zm1oLO1FMyImoPO9PY4l7BZOeqCRk8Fh5xaskeyVGuwr+GzpHYFK46okipEumVBwBTHxxmsXU1xKhxSF3Qg+gTAv2R9QQTctai8mQDZ+n57f4IWu8EQSQTHopGeWRQILDd38yWdtGSKtKIDLyjQdhIqFCYRC3yFi2mSaJbpdSobEDAAiCUBf1Y7h+COnzh6J0Lg1ElIam0xOx0x8ECeCucrXtWzz46TmREAheyiglBpcCQygN3Cak19KJzT+zL/b11djFNeVISS89n9IcZtx8zvd/fWA4QXooGE194rY5RCI0fHdj5lD3iFd0nDutnJhYihXVYnmHwCn8kaVEWBtAsTgENYT8OkbJ6H+fBJfXo+sEQMGLm3xKUEYqfa6X7g3afwiOZ/Lyu8yDFIamQjFSjJUIwTKND3cOwvazvIoGKZJ4j4BuIJAMsMzVcE 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 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/tru= ncate.c?h=3Dmm-stable#n282 > > Fixes: 7460b470a131f ("mm/truncate: use folio_split() in truncate operati= on") > 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, l= off_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 =3D start; - break; - } + folio_unlock(folio); + index =3D start; + break; } else { /* * Splitting failed, but the part in the --=20 Best Regards, Yan, Zi