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Tue, 13 May 2025 08:38:40 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Suren Baghdasaryan Date: Tue, 13 May 2025 08:38:28 -0700 X-Gm-Features: AX0GCFu_sNznUsLr1ugO_DiPLuhx2Qpcv2QmJwH3d9RiFtZ1VEMUc2w3eNQQQs0 Message-ID: Subject: Re: [PATCH v2 3/3] mm/vma: remove mmap() retry merge To: "Liam R. Howlett" , Lorenzo Stoakes , Andrew Morton , David Hildenbrand , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , Christian Brauner , Jan Kara , Matthew Wilcox Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 43980A000F X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: s3y44dqm8pfsmuf5nujbrqcmd9rjizoc X-HE-Tag: 1747150722-28962 X-HE-Meta: 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 V3QHUXKN 10hySS4y5uysq0ieNCuZ4DLT3KnH7N7qdYB1m9OLVGYg4PGvRNteVPfRIurKk88mcPvwPyfwTBRgAbrVPJgOexQ7FwM29Rq/sJD7bUm9U5eWZrgVAycgL3YOKGzy/+I6Ee5wG/yORvgNZ0n8USm6ko21kponsj8ou7H0ZfJ2E1K7NG7GfD9rsaXkdDpSNHS83ksCUrpv0wXP+QH3orDUoedBPkZ/z0jYTbTfNMqf0rOBXyJb8snXdsgEZ34BSMbyI9WKze1bW6Erk3ug= 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: List-Subscribe: List-Unsubscribe: On Tue, May 13, 2025 at 6:25=E2=80=AFAM Liam R. Howlett wrote: > > * Lorenzo Stoakes [250509 08:14]: > > We have now introduced a mechanism that obviates the need for a reattem= pted > > merge via the mmap_prepare() file hook, so eliminate this functionality > > altogether. > > > > The retry merge logic has been the cause of a great deal of complexity = in > > the past and required a great deal of careful manoeuvring of code to en= sure > > its continued and correct functionality. > > > > It has also recently been involved in an issue surrounding maple tree > > state, which again points to its problematic nature. > > > > We make it much easier to reason about mmap() logic by eliminating this= and > > simply writing a VMA once. This also opens the doors to future optimisa= tion > > and improvement in the mmap() logic. > > > > For any device or file system which encounters unwanted VMA fragmentati= on > > as a result of this change (that is, having not implemented .mmap_prepa= re > > hooks), the issue is easily resolvable by doing so. > > > > Signed-off-by: Lorenzo Stoakes > > Reviewed-by: David Hildenbrand > > I have a few tests for the vma test suite that would test this path. > I'll just let them go. > > Reviewed-by: Liam R. Howlett Reviewed-by: Suren Baghdasaryan > > > --- > > mm/vma.c | 14 -------------- > > 1 file changed, 14 deletions(-) > > > > diff --git a/mm/vma.c b/mm/vma.c > > index 3f32e04bb6cc..3ff6cfbe3338 100644 > > --- a/mm/vma.c > > +++ b/mm/vma.c > > @@ -24,7 +24,6 @@ struct mmap_state { > > void *vm_private_data; > > > > unsigned long charged; > > - bool retry_merge; > > > > struct vm_area_struct *prev; > > struct vm_area_struct *next; > > @@ -2417,8 +2416,6 @@ static int __mmap_new_file_vma(struct mmap_state = *map, > > !(map->flags & VM_MAYWRITE) && > > (vma->vm_flags & VM_MAYWRITE)); > > > > - /* If the flags change (and are mergeable), let's retry later. */ > > - map->retry_merge =3D vma->vm_flags !=3D map->flags && !(vma->vm_f= lags & VM_SPECIAL); Could we have a WARN_ON() here please? I know you took care of in-tree drivers but if an out-of-tree driver does this there will be no indication that it has to change its ways. I know we don't care about out-of-tree ones but they still exist, so maybe we can be nice here and issue a warning? > > map->flags =3D vma->vm_flags; > > > > return 0; > > @@ -2622,17 +2619,6 @@ static unsigned long __mmap_region(struct file *= file, unsigned long addr, > > if (have_mmap_prepare) > > set_vma_user_defined_fields(vma, &map); > > > > - /* If flags changed, we might be able to merge, so try again. */ > > - if (map.retry_merge) { > > - struct vm_area_struct *merged; > > - VMG_MMAP_STATE(vmg, &map, vma); > > - > > - vma_iter_config(map.vmi, map.addr, map.end); > > - merged =3D vma_merge_existing_range(&vmg); > > - if (merged) > > - vma =3D merged; > > - } > > - > > __mmap_complete(&map, vma); > > > > return addr; > > -- > > 2.49.0 > >