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b=LPN5XdK4RD/9ann95QRaRMH8iwCmfE4xqsiUbUaSIFW1gOQAi3jvkAPFy9Ne/gex0 DLq3806t9o1ar6v61LMZvyQHR3hlaHI531/DnVgdpM8gBvebmMS1SSs+MmtDFG8f9N Z4VyTuW22OeWZX3cNF5LJ3Vi+wmPMYHZUGl/hvW4fBr1moDmQjsf1ioBivxDYGR74a vyLnb4EsN2jQDcPqNOXaOBp3xiaMmZtv74phnPa3SzZrYDty8Ptd3siyGMFLg/3awr HSMV8IVunt+MYsHoKG/Yb37zdRfQwhqtarfQlqv1BrvHDRz/zymKfcNiS8TGUN5r9F /8h4M49rEjnhg== Date: Tue, 10 Mar 2026 08:19:20 +0000 From: "Lorenzo Stoakes (Oracle)" To: Dev Jain Cc: akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, david@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com, weixugc@google.com, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, pfalcato@suse.de, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, baohua@kernel.org, youngjun.park@lge.com, ziy@nvidia.com, kas@kernel.org, willy@infradead.org, yuzhao@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com Subject: Re: [PATCH 3/9] mm/rmap: refactor lazyfree unmap commit path to commit_ttu_lazyfree_folio() Message-ID: <3915e3bc-c390-44bc-a463-bdd687598284@lucifer.local> References: <20260310073013.4069309-1-dev.jain@arm.com> <20260310073013.4069309-4-dev.jain@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260310073013.4069309-4-dev.jain@arm.com> X-Rspam-User: X-Stat-Signature: 5pjtwi8mxhgs89tqiiuyjx8t8mzeaez1 X-Rspamd-Queue-Id: 3607414000F X-Rspamd-Server: rspam03 X-HE-Tag: 1773130771-916926 X-HE-Meta: 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 10, 2026 at 01:00:07PM +0530, Dev Jain wrote: > Clean up the code by refactoring the post-pte-clearing path of lazyfree > folio unmapping, into commit_ttu_lazyfree_folio(). > > No functional change is intended. > > Signed-off-by: Dev Jain This is a good idea, and we need more refactoring like this in the rmap code, but comments/nits below. > --- > mm/rmap.c | 93 ++++++++++++++++++++++++++++++++----------------------- > 1 file changed, 54 insertions(+), 39 deletions(-) > > diff --git a/mm/rmap.c b/mm/rmap.c > index 1fa020edd954a..a61978141ee3f 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1966,6 +1966,57 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio, > FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY); > } > > +static inline int commit_ttu_lazyfree_folio(struct vm_area_struct *vma, Strange name, maybe lazyfree_range()? Not sure what ttu has to do with anything... > + struct folio *folio, unsigned long address, pte_t *ptep, > + pte_t pteval, long nr_pages) That long nr_pages is really grating now... > +{ Come on Dev, it's 2026, why on earth are you returning an integer and not a bool? Also it would make sense for this to return false if something breaks, otherwise true. > + struct mm_struct *mm = vma->vm_mm; > + int ref_count, map_count; > + > + /* > + * Synchronize with gup_pte_range(): > + * - clear PTE; barrier; read refcount > + * - inc refcount; barrier; read PTE > + */ > + smp_mb(); > + > + ref_count = folio_ref_count(folio); > + map_count = folio_mapcount(folio); > + > + /* > + * Order reads for page refcount and dirty flag > + * (see comments in __remove_mapping()). > + */ > + smp_rmb(); > + > + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { > + /* > + * redirtied either using the page table or a previously > + * obtained GUP reference. > + */ > + set_ptes(mm, address, ptep, pteval, nr_pages); > + folio_set_swapbacked(folio); > + return 1; > + } > + > + if (ref_count != 1 + map_count) { > + /* > + * Additional reference. Could be a GUP reference or any > + * speculative reference. GUP users must mark the folio > + * dirty if there was a modification. This folio cannot be > + * reclaimed right now either way, so act just like nothing > + * happened. > + * We'll come back here later and detect if the folio was > + * dirtied when the additional reference is gone. > + */ > + set_ptes(mm, address, ptep, pteval, nr_pages); > + return 1; > + } > + > + add_mm_counter(mm, MM_ANONPAGES, -nr_pages); > + return 0; > +} > + > /* > * @arg: enum ttu_flags will be passed to this argument > */ > @@ -2227,46 +2278,10 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, > > /* MADV_FREE page check */ > if (!folio_test_swapbacked(folio)) { > - int ref_count, map_count; > - > - /* > - * Synchronize with gup_pte_range(): > - * - clear PTE; barrier; read refcount > - * - inc refcount; barrier; read PTE > - */ > - smp_mb(); > - > - ref_count = folio_ref_count(folio); > - map_count = folio_mapcount(folio); > - > - /* > - * Order reads for page refcount and dirty flag > - * (see comments in __remove_mapping()). > - */ > - smp_rmb(); > - > - if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { > - /* > - * redirtied either using the page table or a previously > - * obtained GUP reference. > - */ > - set_ptes(mm, address, pvmw.pte, pteval, nr_pages); > - folio_set_swapbacked(folio); > + if (commit_ttu_lazyfree_folio(vma, folio, address, > + pvmw.pte, pteval, > + nr_pages)) With above corrections this would be: if (!lazyfree_range(vma, folio, address, pvme.pte, pteval, nr_pages)) ... > goto walk_abort; > - } else if (ref_count != 1 + map_count) { > - /* > - * Additional reference. Could be a GUP reference or any > - * speculative reference. GUP users must mark the folio > - * dirty if there was a modification. This folio cannot be > - * reclaimed right now either way, so act just like nothing > - * happened. > - * We'll come back here later and detect if the folio was > - * dirtied when the additional reference is gone. > - */ > - set_ptes(mm, address, pvmw.pte, pteval, nr_pages); > - goto walk_abort; > - } > - add_mm_counter(mm, MM_ANONPAGES, -nr_pages); > goto discard; > } > > -- > 2.34.1 > Thanks, Lorenzo