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b=iLrKqB5rvvFeu94eo3XrsentSFfG/eI+jaIFbWU3IqN1+FuG73fdGExozgmxXVYnX Hf2AvgrjbGrchMF/wL/RRio4aT+F2HFswp5XWqfs/6q8KXUNIZHDDGwr5fWyjFmBCv HZpV3HA43DjzuJPMVm+jZ4HBtfSztnJrMnnbeFeog04nijPPxlODilc+/g42O4At/O lnY3WEF3wfbKZZjnKwI6SGF7JXCOgsL/QGnHoAEQXRWHiVqyiLCGbcI2H77tkP+7wx uMjE4G8z55XPM6fbN+4Z5F8tsAHaeruruAnU7nOARa7Sg+cO2Ay7LxcBSuffDA/kMs ty/7AjxNeVpQw== Message-ID: Date: Mon, 11 May 2026 09:28:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/9] mm/rmap: refactor some code around lazyfree folio unmapping To: Dev Jain , akpm@linux-foundation.org, ljs@kernel.org, hughd@google.com, chrisl@kernel.org, kasong@tencent.com Cc: riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, rppt@kernel.org, surenb@google.com, mhocko@suse.com, baolin.wang@linux.alibaba.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, pfalcato@suse.de, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260506094504.2588857-1-dev.jain@arm.com> <20260506094504.2588857-4-dev.jain@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: E4973180007 X-Stat-Signature: ti1dznwg3ooqrh8db31zzxg69n6dkc46 X-HE-Tag: 1778484513-37677 X-HE-Meta: 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 QCSWrW81 XHMfk0YGGSSMO2NT7Hnc79EKrQxdvqhrgS+PKbNWZaQKYzhfuDwtQlGD9IuH1Wfj+jqLDcG4hYfGnLAkcpw45DjFQX0pjK6OUbRZ2LUf5l4ejHsQsZgyFaVRRmvHxOFDEAV0NMDSCyx2223k7LLCvHSihD8cgG7DrGQUvxVvAKusPn42PllfaFPQwwo1BS+jHD1AeA82+HVYhWmIvBJIJGxwriiT7ByOPrnC4MaMeLCggF4H37QKBw8tYy5q4oX1qlmC6apk8in88H/78VC4aEFLkkqQCO4mhU6sk+1qbA1dV1Rqy65PjoudYOAuVzjsVBvW9 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/6/26 11:44, Dev Jain wrote: > For lazyfree folio unmapping, after clearing the ptes we must abort the > operation if the folio got dirtied or it has unexpected references. > > Refactor this logic into a function which will return whether we need > to abort or not. > > If we abort, we restore the ptes and bail out of try_to_unmap_one. > Otherwise adjust the rss stats of the mm and jump to a label. > > Also rename that label from "discard" to "finish_unmap"; the former > is appropriate in the lazyfree context, but the code following the label > is executed for other successful unmap code paths too, so 'discard' does > not sound correct for them. > > Signed-off-by: Dev Jain > --- > mm/rmap.c | 95 ++++++++++++++++++++++++++++++++----------------------- > 1 file changed, 55 insertions(+), 40 deletions(-) > > diff --git a/mm/rmap.c b/mm/rmap.c > index a98acdea0530a..bd4e3639e26ed 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1978,6 +1978,56 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio, > FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY); > } > > +static inline bool can_unmap_lazyfree_folio_range(struct vm_area_struct *vma, > + struct folio *folio, unsigned long address, pte_t *ptep, > + pte_t pteval, unsigned long nr_pages) Similar comment: ttu_...* > +{ > + 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 false; > + } > + > + 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 false; > + } > + > + return true; Doing the set_ptes() in a function called "can_unmap_lazyfree_folio_range" is not appropriate. Can we just leave that in the caller? We only do the when we return false. And hey, then you can call this function ttu_can_unmap_lazyfree_folio() and avoid passing pte ranges. :) -- Cheers, David