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b=EZJihxwOpVWFeeznrgLeQqSQeTk7yq8IelzVwu+39gwCLwmKIMbWCLVS8g72Cy6qg 0V4XSfEnj7oPw551RgFyyULnCllILRZxqw/cVQMhhe2ALmi6Mv8v5c7SVG72tFbaLO LILkb++w8XSq97YrJyZtfTnHPkHr0wRwDDVoAmtzEjO9GS62IeS18+LKzZ+EPQNdM0 TMbLsjNJJGgs4B8DJDa29+rPlPjfR+xLXwHsJgr61/+JHTez2hBD0BBn24esaxx9ht ENKQLjrEgDlCADpUa7uNzqyvd0xZC1YRnVqUiR213BDbrrdPECYPwg67jaa9NmHurY HhKmo+HqJzQHQ== Message-ID: <95b8224d-3ed4-4fe3-9954-d5ba0aa373f8@kernel.org> Date: Mon, 11 May 2026 10:13:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 8/9] mm/rmap: Add batched version of folio_try_share_anon_rmap_pte 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> <20260506094504.2588857-9-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-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 5E4E780008 X-Stat-Signature: b4eem33gct68x1atsrrxmaami9uyx9u7 X-Rspam-User: X-HE-Tag: 1778487202-137198 X-HE-Meta: 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 8fLc2Zfi YGDeVXKY+VITzFrDC+fOZT/WfLUVAYGOBdHTwyOhqtO3cvIEH8vDzkCyQrk9b8/IpvG7yj8uJgGHCodPyESbc+dhmqPwjG4AJTjWROi7w5QpjBUMqvqNbNQqs9KmC1X4KC8HEtnRsS6lneXURR4ZIlNluDXGTmCcln1PTzc91U6Fd6tyv2ZRz8bOvqKiue4ds0z4HWiaFGk0Oc9yjK9Zjagc+pl1MRL3YcYu+/0PKakej8JCp+5JHY9QN5RQByoFd17oDD/dor/aO1TMGVOYakDdSTPEcPjPwhnGmDWuDBF0a3VYuYnwkpD0DJPLMYsUYFjGucQiYlZjIgoyfK3qvTVawS5BydZ3YIurlCOBT7I9WKjPelH1KBTRfHhfqWPjwa0sR5kzt19T1CqE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/6/26 11:45, Dev Jain wrote: > To enable batched unmapping of anonymous folios, we need to handle the > sharing of exclusive pages. Hence, a batched version of > folio_try_share_anon_rmap_pte is required. > > Currently, the sole purpose of nr_pages in __folio_try_share_anon_rmap is > to do some rmap sanity checks. Add helpers to clear the PageAnonExclusive > bit on a batch of nr_pages. Note that __folio_try_share_anon_rmap can > receive nr_pages == HPAGE_PMD_NR from the PMD path, but currently we only > clear the bit on the head page. Retain this behaviour by setting > nr_pages = 1 in case the caller is folio_try_share_anon_rmap_pmd. > > While at it, convert nr_pages to unsigned long to future-proof from > overflow in case P4D-huge mappings etc get supported down the road. > I haven't made such a change in each function receiving nr_pages in > try_to_unmap_one - perhaps this can be done incrementally. > > Signed-off-by: Dev Jain > --- > include/linux/mm.h | 11 +++++++++++ > include/linux/rmap.h | 27 ++++++++++++++++++++------- > 2 files changed, 31 insertions(+), 7 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 31e27ff6a35fa..0b77329cf57a4 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -243,6 +243,17 @@ static inline unsigned long folio_page_idx(const struct folio *folio, > return page - &folio->page; > } > > +static __always_inline void folio_clear_pages_anon_exclusive(struct page *page, > + unsigned long nr_pages) > +{ > + for (;;) { > + ClearPageAnonExclusive(page); > + if (--nr_pages == 0) > + break; > + ++page; > + } > +} Something called folio that doesn't consume a folio is odd. I'd prefer we don't add this. Is there a chance to simply change __folio_try_share_anon_rmap, so we get a single loop inline? diff --git a/include/linux/rmap.h b/include/linux/rmap.h index 8dc0871e5f00..5a1c874b2112 100644 --- a/include/linux/rmap.h +++ b/include/linux/rmap.h @@ -708,16 +708,13 @@ static inline int folio_try_dup_anon_rmap_pmd(struct folio *folio, static __always_inline int __folio_try_share_anon_rmap(struct folio *folio, struct page *page, int nr_pages, enum pgtable_level level) { + /* device private folios cannot get pinned via GUP. */ + const bool pinnable = !folio_is_device_private(folio); + VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); VM_WARN_ON_FOLIO(!PageAnonExclusive(page), folio); __folio_rmap_sanity_checks(folio, page, nr_pages, level); - /* device private folios cannot get pinned via GUP. */ - if (unlikely(folio_is_device_private(folio))) { - ClearPageAnonExclusive(page); - return 0; - } - /* * We have to make sure that when we clear PageAnonExclusive, that * the page is not pinned and that concurrent GUP-fast won't succeed in @@ -760,19 +757,21 @@ static __always_inline int __folio_try_share_anon_rmap(struct folio *folio, * so we use explicit ones here. */ - /* Paired with the memory barrier in try_grab_folio(). */ - if (IS_ENABLED(CONFIG_HAVE_GUP_FAST)) - smp_mb(); + if (pinnable) { + /* Paired with the memory barrier in try_grab_folio(). */ + if (IS_ENABLED(CONFIG_HAVE_GUP_FAST)) + smp_mb(); - if (unlikely(folio_maybe_dma_pinned(folio))) - return -EBUSY; + if (unlikely(folio_maybe_dma_pinned(folio))) + return -EBUSY; + } ClearPageAnonExclusive(page); /* * This is conceptually a smp_wmb() paired with the smp_rmb() in * gup_must_unshare(). */ - if (IS_ENABLED(CONFIG_HAVE_GUP_FAST)) + if (pinnable && IS_ENABLED(CONFIG_HAVE_GUP_FAST)) smp_mb__after_atomic(); return 0; -- Cheers, David