From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 047D0313E07 for ; Thu, 9 Jul 2026 13:43:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783604637; cv=none; b=o2wZxGyKVTsHuln9tjlUbuqItlEhX13irgvJuMWBp9Tc+ocLC+BB/Vpdrrxu11dehHnUKymty3mG2J2J5oLx3sie86mqwsaCL4Xl9BTVg6BZ5hK8p2r3rHf7DS5J+FnG0JPlioQA+B2AJB1aNQG4TDlNfXyLIoZNMkvolJufs60= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783604637; c=relaxed/simple; bh=M+VeTYGcTAYLwLjIetUGwufi/dijV84F+IViyrXJsC8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LNS+8i3uhkhnAoypSukk3wpXzJV1rWAvAYyv2zp/AQ+jm03F3sn274FFAwydq/JThNHKotRsXDWSAowlSA3OC84io/6zG0EN3B6ndcKWtEtojPZT3021UWWx4P6iSnUqXOFdMCq+OVxVRkYxIIEfDndUfErdbcf2n8pa/UKVnm0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=opk4Zayp; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="opk4Zayp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BA4C61F000E9; Thu, 9 Jul 2026 13:43:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783604635; bh=XOhwLdFtYZrbNxPNuQ1ybZBGzEAMmXkIAYF778B+TdM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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 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 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 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