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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] mm: propagate VM_SOFTDIRTY on merge Message-Id: <20251117145413.badc72b4bbddc0978c64c3eb@linux-foundation.org> In-Reply-To: <955478b5170715c895d1ef3b7f68e0cd77f76868.1763399675.git.lorenzo.stoakes@oracle.com> References: <955478b5170715c895d1ef3b7f68e0cd77f76868.1763399675.git.lorenzo.stoakes@oracle.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 4A60E180008 X-Stat-Signature: 1ohbfb6snh56o5nu95qxq93qn6ry6z9h X-Rspam-User: X-HE-Tag: 1763420058-913311 X-HE-Meta: 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 7hEKIH9h XmitB 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 Mon, 17 Nov 2025 17:33:38 +0000 Lorenzo Stoakes wrote: > Currently we set VM_SOFTDIRTY when a new mapping is set up (whether by > establishing a new VMA, or via merge) as implemented in __mmap_complete() > and do_brk_flags(). > > However, when performing a merge of existing mappings such as when > performing mprotect(), we may lose the VM_SOFTDIRTY flag. > > This is because currently we simply ignore VM_SOFTDIRTY for the purposes > of merge, so one VMA may possess the flag and another not, and whichever > happens to be the target VMA will be the one upon which the merge is > performed which may or may not have VM_SOFTDIRTY set. > > Now we have the concept of 'sticky' VMA flags, let's make VM_SOFTDIRTY one > which solves this issue. > > Additionally update VMA userland tests to propagate changes. > Oh. This patch messes with the comments which mm-implement-sticky-vma-flags-fix-2.patch just altered. Not sure what you intend here, so I left it as below - please advise. (also, I fixed a typo: s/most/must/, both files) --- a/include/linux/mm.h~mm-propagate-vm_softdirty-on-merge +++ a/include/linux/mm.h @@ -532,28 +532,28 @@ extern unsigned int kobjsize(const void * possesses it but the other does not, the merged VMA should nonetheless have * applied to it: * + * VM_SOFTDIRTY - if a VMA is marked soft-dirty, that is has not had its + * references cleared via /proc/$pid/clear_refs, any merged VMA + * should be considered soft-dirty also as it operates at a VMA + * granularity. + * * VM_MAYBE_GUARD - If a VMA may have guard regions in place it implies that * mapped page tables may contain metadata not described by the * VMA and thus any merged VMA may also contain this metadata, * and thus we must make this flag sticky. */ -#define VM_STICKY VM_MAYBE_GUARD +#define VM_STICKY (VM_SOFTDIRTY | VM_MAYBE_GUARD) /* * VMA flags we ignore for the purposes of merge, i.e. one VMA possessing one * of these flags and the other not does not preclude a merge. * - * VM_SOFTDIRTY - Should not prevent from VMA merging, if we match the flags but - * dirty bit -- the caller should mark merged VMA as dirty. If - * dirty bit won't be excluded from comparison, we increase - * pressure on the memory system forcing the kernel to generate - * new VMAs when old one could be extended instead. - * - * VM_STICKY - When merging VMAs, VMA flags must match, unless they are - * 'sticky'. If any sticky flags exist in either VMA, we simply - * set all of them on the merged VMA. + * VM_STICKY - If one VMA has flags which must be 'sticky', that is ones + * which should propagate to all VMAs, but the other does not, + * the merge should still proceed with the merge logic applying + * sticky flags to the final VMA. */ -#define VM_IGNORE_MERGE (VM_SOFTDIRTY | VM_STICKY) +#define VM_IGNORE_MERGE VM_STICKY /* * Flags which should result in page tables being copied on fork. These are --- a/tools/testing/vma/vma_internal.h~mm-propagate-vm_softdirty-on-merge +++ a/tools/testing/vma/vma_internal.h @@ -122,28 +122,23 @@ extern unsigned long dac_mmap_min_addr; * possesses it but the other does not, the merged VMA should nonetheless have * applied to it: * - * VM_MAYBE_GUARD - If a VMA may have guard regions in place it implies that - * mapped page tables may contain metadata not described by the - * VMA and thus any merged VMA may also contain this metadata, - * and thus we must make this flag sticky. + * VM_SOFTDIRTY - if a VMA is marked soft-dirty, that is has not had its + * references cleared via /proc/$pid/clear_refs, any merged VMA + * should be considered soft-dirty also as it operates at a VMA + * granularity. */ -#define VM_STICKY VM_MAYBE_GUARD +#define VM_STICKY (VM_SOFTDIRTY | VM_MAYBE_GUARD) /* * VMA flags we ignore for the purposes of merge, i.e. one VMA possessing one * of these flags and the other not does not preclude a merge. * - * VM_SOFTDIRTY - Should not prevent from VMA merging, if we match the flags but - * dirty bit -- the caller should mark merged VMA as dirty. If - * dirty bit won't be excluded from comparison, we increase - * pressure on the memory system forcing the kernel to generate - * new VMAs when old one could be extended instead. - * - * VM_STICKY - When merging VMAs, VMA flags must match, unless they are - * 'sticky'. If any sticky flags exist in either VMA, we simply - * set all of them on the merged VMA. + * VM_STICKY - If one VMA has flags which most be 'sticky', that is ones + * which should propagate to all VMAs, but the other does not, + * the merge should still proceed with the merge logic applying + * sticky flags to the final VMA. */ -#define VM_IGNORE_MERGE (VM_SOFTDIRTY | VM_STICKY) +#define VM_IGNORE_MERGE VM_STICKY /* * Flags which should result in page tables being copied on fork. These are _