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b=opk4ZaypYNn9jx52A8N60MT57hnfGw1hnMsgqYVIxo1XlOTLoHdMx5fcV9lUue9qC HdocdJgxmzULWj+0Uw7XO2vy2aUZWsYZfum38cUa3IqMvxnJqO994JxLeLsIk8NuWw d5FeERIIjC35baqIcyWRyEeiSK0xa+4Uq+58SI3PYt/2e9JFsNBCTZdvzJw3fljnqy StlMEuC0DJlX0Hvj/gdmflHpR6htmgduIwSyZc3/FiFGpRMITW17KLAvBIYG+esxfd HfLXocmEUvk7edI3KedeCSkISrf+7FDEH9BOLWmaTm0VwHZP+PKF9IfvffAzaXWWjY 20TDkN4pCdccw== Message-ID: <1d6732f3-af7f-4487-b704-626d5bc52843@kernel.org> Date: Thu, 9 Jul 2026 15:43:49 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/5] mm/rmap: refactor some code around lazyfree folio unmapping To: Dev Jain , akpm@linux-foundation.org, ljs@kernel.org, muchun.song@linux.dev, osalvador@suse.de Cc: riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260707121128.373192-1-dev.jain@arm.com> <20260707121128.373192-4-dev.jain@arm.com> <22fb2f54-da23-40b2-91f5-aeaf54037bcd@kernel.org> <61fb2165-bc58-4c54-84b2-4ada10b19bcf@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: A0FE940007 X-Stat-Signature: pwajcits1dtqcy5i3k3jws8kdmfwxkyp X-HE-Tag: 1783604636-506496 X-HE-Meta: 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 GFwYmWJG 6AJmheJS+RnGVMzYb6Xp7GSN/qbGEXCaxg6krFhVmrMRZnvfe075+QDNoK7EG94YjPzrAxBr2WWg+ZbWJy8N1vuhiQv2Pd3p2PWpUOWLQUkLN0CP4fKIEcz3dEeY014fo+NHDyUq/U5/LQQPErO4Cubyp3jXc8WJKvgfsSpjfnNg2gPPXWufKQIjzc2P+3gCKwmjcsLskNwD2j9t8e07QDFwRuDPObGm2pUKlEbsnrnxIQdP1n9IUae6N8SAErlmaYUq/tExvso/ZVbKzZX+DpyyoVoiqX/9Cj867boDSLMlaElTju2FKd6z3zv9VkA+yI0A5 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/9/26 14:16, Dev Jain wrote: > > > On 07/07/26 7:48 pm, David Hildenbrand (Arm) wrote: >> On 7/7/26 14:11, 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. >>> >>> No functional change intended. >>> >>> Signed-off-by: Dev Jain >>> --- >>> mm/rmap.c | 87 +++++++++++++++++++++++++++++++------------------------ >>> 1 file changed, 49 insertions(+), 38 deletions(-) >>> >>> diff --git a/mm/rmap.c b/mm/rmap.c >>> index 934773dfa2f2a..00b571c2a1bab 100644 >>> --- a/mm/rmap.c >>> +++ b/mm/rmap.c >>> @@ -2067,6 +2067,52 @@ static bool try_to_unmap_hugetlb_one(struct folio *folio, >>> return ret; >>> } >>> >>> +static inline bool ttu_anon_lazyfree_folio(struct vm_area_struct *vma, >>> + struct folio *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. >>> + */ >>> + 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. >>> + */ >>> + return false; >>> + } >>> + >>> + return true; >> >> You could simply do >> >> >> /* >> * Additional references could be due to GUP or from a speculative >> * lookup. ... > > Are you also suggesting to shorten the comment? To reduce its indentation and then comment on the conditional "Additional references could be due to GUP or from a speculative .." Instead of "Additional reference." -- Cheers, David