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Shutemov" , Jerome Glisse , Alistair Popple , Miaohe Lin , Matthew Wilcox , Axel Rasmussen Subject: [PATCH v4 1/4] mm/shmem: Unconditionally set pte dirty in mfill_atomic_install_pte Date: Wed, 15 Sep 2021 14:14:53 -0400 Message-Id: <20210915181456.10739-2-peterx@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210915181456.10739-1-peterx@redhat.com> References: <20210915181456.10739-1-peterx@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="US-ASCII" Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=cKOlx5KA; spf=none (imf30.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: B96B7E001987 X-Stat-Signature: pjjeu138j5kbc89dm156ujwcztmn1kxx X-HE-Tag: 1631729703-285733 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: It was conditionally done previously, as there's one shmem special case t= hat we use SetPageDirty() instead. However that's not necessary and it should b= e easier and cleaner to do it unconditionally in mfill_atomic_install_pte()= . The most recent discussion about this is here, where Hugh explained the h= istory of SetPageDirty() and why it's possible that it's not required at all: https://lore.kernel.org/lkml/alpine.LSU.2.11.2104121657050.1097@eggly.anv= ils/ Currently mfill_atomic_install_pte() has three callers: 1. shmem_mfill_atomic_pte 2. mcopy_atomic_pte 3. mcontinue_atomic_pte After the change: case (1) should have its SetPageDirty replaced by the d= irty bit on pte (so we unify them together, finally), case (2) should have no functional change at all as it has page_in_cache=3D=3Dfalse, case (3) may= add a dirty bit to the pte. However since case (3) is UFFDIO_CONTINUE for shme= m, it's merely 100% sure the page is dirty after all because UFFDIO_CONTINUE normally requires another process to modify the page cache and kick the f= aulted thread, so should not make a real difference either. This should make it much easier to follow on which case will set dirty fo= r uffd, as we'll simply set it all now for all uffd related ioctls. Meanwh= ile, no special handling of SetPageDirty() if there's no need. Cc: Hugh Dickins Cc: Axel Rasmussen Cc: Andrea Arcangeli Reviewed-by: Axel Rasmussen Signed-off-by: Peter Xu --- mm/shmem.c | 1 - mm/userfaultfd.c | 3 +-- 2 files changed, 1 insertion(+), 3 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index 88742953532c..96ccf6e941aa 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2424,7 +2424,6 @@ int shmem_mfill_atomic_pte(struct mm_struct *dst_mm= , shmem_recalc_inode(inode); spin_unlock_irq(&info->lock); =20 - SetPageDirty(page); unlock_page(page); return 0; out_delete_from_cache: diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 7a9008415534..caf6dfff2a60 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -69,10 +69,9 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm,= pmd_t *dst_pmd, pgoff_t offset, max_off; =20 _dst_pte =3D mk_pte(page, dst_vma->vm_page_prot); + _dst_pte =3D pte_mkdirty(_dst_pte); if (page_in_cache && !vm_shared) writable =3D false; - if (writable || !page_in_cache) - _dst_pte =3D pte_mkdirty(_dst_pte); if (writable) { if (wp_copy) _dst_pte =3D pte_mkuffd_wp(_dst_pte); --=20 2.31.1