From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C499F442106; Fri, 31 Jul 2026 17:53:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785520397; cv=none; b=JqZs1iCDypuYPcndWlD/NzSKIza41VJY/fegwUqwx+U/AvJ0JEPAlzQJE/MYxdulN1WwHlftGIlM+cRhXTAJNXk0koWNnPUCz6dxYaSEGOuyDPMjDmp11TClU7od+ls0COn1+gLX4QgAKdduPRXYi/5i2I3M2wLRM+F0voD+TlU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785520397; c=relaxed/simple; bh=FkA5oFEShK23UmRSU9gc0ugvAETJkWARmPyTi18l0lY=; h=Date:To:From:Subject:Message-Id; b=gmtEp6Wvsizc/hc3ek7mdVB+bqRFlWx1hHlkUAx8dyqTCz0CX3eVUvyoAYhPaHzzn7++KmQCfnpd6JSgi/jTn9vMtFqQoMqc7S+J4+6lk2fSofyQteseY4Hu9zNCqKxInYPR4jEecBDPHRiWT37TaH4Zj0Scde43PN4XO+ZiKRA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=GfNhDTbo; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="GfNhDTbo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DB4FC1F00ACA; Fri, 31 Jul 2026 17:53:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1785520395; bh=6c9iDN37jDA8XOCofqdqgwTjdoRk9RxVZQOwtoN4qpE=; h=Date:To:From:Subject; b=GfNhDTbose38OCkSGqhvYqtwkxEy2zTCdd37vOOFYvw/pwirovrqLfKPYJ/ov9cMx L9aqWtz1dy4REAf0dq5bnCdUkKgs2Y/OhpDCDLPFCDxRw98XTHob9mc432bE8EWiMT IbmkhlKG8cI0RyNnzarq+7nolQ4r4dSuudGOTyz4= Date: Fri, 31 Jul 2026 10:53:14 -0700 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,riel@surriel.com,osalvador@suse.de,muchun.song@linux.dev,leitao@debian.org,david@kernel.org,guillaume@morinfr.org,akpm@linux-foundation.org From: Andrew Morton Subject: + hugetlb-only-adjust-reservation-during-unmapping-if-mapcount-is-0.patch added to mm-new branch Message-Id: <20260731175314.DB4FC1F00ACA@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: hugetlb: only adjust reservation during unmapping if mapcount is 0 has been added to the -mm mm-new branch. Its filename is hugetlb-only-adjust-reservation-during-unmapping-if-mapcount-is-0.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/hugetlb-only-adjust-reservation-during-unmapping-if-mapcount-is-0.patch This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next If a few days of testing in mm-new is successful, the patch will me moved into mm.git's mm-unstable branch, which is included in linux-next Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Guillaume Morin Subject: hugetlb: only adjust reservation during unmapping if mapcount is 0 Date: Tue, 28 Jul 2026 21:29:03 +0200 Since df7a6d1f6405, __unmap_hugepage_range can adjust reservations. In the case of folio mapped in both a parent and a child, if the parent unmaps the range first, the reservation adjustment will result in an underflow of the reserved count. Once the child unmaps the range, the count is restored. Change __unmap_hugepage_range() to check the mapcount before adjusting the reservation. Link: https://lore.kernel.org/all/alEJkwn5VlTTH_ZX@bender.morinfr.org/ Link: https://lore.kernel.org/amkC_1Ya6OiUoiLZ@bender.morinfr.org Fixes: df7a6d1f6405 ("mm/hugetlb: restore the reservation if needed") Signed-off-by: Guillaume Morin Reviewed-by: Breno Leitao Reviewed-by: Rik van Riel Cc: Muchun Song Cc: David Hildenbrand Cc: Oscar Salvador Cc: Signed-off-by: Andrew Morton --- mm/hugetlb.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/mm/hugetlb.c~hugetlb-only-adjust-reservation-during-unmapping-if-mapcount-is-0 +++ a/mm/hugetlb.c @@ -5218,6 +5218,7 @@ void __unmap_hugepage_range(struct mmu_g bool adjust_reservation; unsigned long last_addr_mask; + i_mmap_assert_write_locked(vma->vm_file->f_mapping); WARN_ON(!is_vm_hugetlb_page(vma)); BUG_ON(start & ~huge_page_mask(h)); BUG_ON(end & ~huge_page_mask(h)); @@ -5309,7 +5310,10 @@ void __unmap_hugepage_range(struct mmu_g /* * Restore the reservation for anonymous page, otherwise the - * backing page could be stolen by someone. + * backing page could be stolen by someone. Restore only on the + * last unmap, otherwise the owner could empty its resv map + * while the folio is still mapped by a child. Note that holding + * i_mmap_lock_write is needed to check the number of mappings. * If there we are freeing a surplus, do not set the restore * reservation bit. */ @@ -5317,7 +5321,7 @@ void __unmap_hugepage_range(struct mmu_g spin_lock_irq(&hugetlb_lock); if (!h->surplus_huge_pages && __vma_private_lock(vma) && - folio_test_anon(folio)) { + !folio_mapped(folio) && folio_test_anon(folio)) { folio_set_hugetlb_restore_reserve(folio); /* Reservation to be adjusted after the spin lock */ adjust_reservation = true; _ Patches currently in -mm which might be from guillaume@morinfr.org are hugetlb-only-adjust-reservation-during-unmapping-if-mapcount-is-0.patch