From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 370E5307494 for ; Mon, 11 May 2026 08:13:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778487203; cv=none; b=Y75ANJZ1VUf6OUPS97p2okcXwIEc++BLxgUa8xJx2xHEIiITAwOCLDpDQXbEgPrF3YPDfTSAWZLOwVRp5fy2f30sIx0yRRNcnEIG7FjErVOUJbQPZOXs5wh6YnbWEtVvdgWuh47cTj3BUhS5U75Lm5WVmwB2gTzvhhjYbe/DD7c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778487203; c=relaxed/simple; bh=t4L0ozuEGJMJPzRYPUeK7nfkUd9Xf55sDSkad6aH9GA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tYRtF9z4gEBoz+OLJaMScvB4J/E1WqIeZZy6Kt2Mm2I+tiwA2IiNUrXdPs/iF+2FWIWDRR6jRoIe/3ZQR+uiZ5RMZ2wLuBiu7hDktQFHbQ7XaSgEKrym3M20rE2CL7q7bWrlmqJV5cbCSO4pmVkreGvnIHqRce5LgIvVzw9NB9M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EZJihxwO; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="EZJihxwO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 019CFC2BCB0; Mon, 11 May 2026 08:13:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778487201; bh=t4L0ozuEGJMJPzRYPUeK7nfkUd9Xf55sDSkad6aH9GA=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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