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 5D8E831355E for ; Mon, 17 Nov 2025 22:54:17 +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=1763420058; cv=none; b=jHMAGjm4os3FLxDg/+5ryVIVTsNAmmeWQFp53eN/O7mwXAtL2aD9jaxv560fUKQJQV85quGX+ubgFQsDRkfnbE2nrWZzmveU4BkeE/AToEads/rUCi4x38L92ELE1Gisn6iE6Z2Th0RZMOk1qCvMj7OiBxV2X4vxuVLxjpEE0UM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763420058; c=relaxed/simple; bh=vdqfGnVe7I9MHRJbwZ176INY948zJgxrzjBYmugLPk0=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=e0iM2zyGU/h2z5jhnKC/m8H5vcseoPIH9f4CADFz2KZa28wHWJMbkbzi0quWMKdzYuZSCl1N5oVsnGS6IrOC4oAaYqCBoA6q6XNjsIEH+v8ftTKnkk5SfvK/lGmQqZ75wRWbjlG7849JltC7TzU6WbiStK36+cuDUZNr3poxnxQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=XgtT73/Q; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="XgtT73/Q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A3734C2BC86; Mon, 17 Nov 2025 22:54:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1763420056; bh=vdqfGnVe7I9MHRJbwZ176INY948zJgxrzjBYmugLPk0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=XgtT73/QnbYISnm8iHaknziIy67cQI178pnbw/AH8EuC9gNLsgmyDdejPUFjCLp0U dRG3unJ13wfib4+NbSaPhdbaDi+RPgq3K2kv3z6eFwZ0SItdiY1/faxqSt/iqceX91 YnQ4mdoYwAhGVECLJmNwNmrmRLqgQL5uLUE0cuDo= Date: Mon, 17 Nov 2025 14:54:13 -0800 From: Andrew Morton To: Lorenzo Stoakes Cc: David Hildenbrand , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] mm: propagate VM_SOFTDIRTY on merge Message-Id: <20251117145413.badc72b4bbddc0978c64c3eb@linux-foundation.org> In-Reply-To: <955478b5170715c895d1ef3b7f68e0cd77f76868.1763399675.git.lorenzo.stoakes@oracle.com> References: <955478b5170715c895d1ef3b7f68e0cd77f76868.1763399675.git.lorenzo.stoakes@oracle.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 17 Nov 2025 17:33:38 +0000 Lorenzo Stoakes wrote: > Currently we set VM_SOFTDIRTY when a new mapping is set up (whether by > establishing a new VMA, or via merge) as implemented in __mmap_complete() > and do_brk_flags(). > > However, when performing a merge of existing mappings such as when > performing mprotect(), we may lose the VM_SOFTDIRTY flag. > > This is because currently we simply ignore VM_SOFTDIRTY for the purposes > of merge, so one VMA may possess the flag and another not, and whichever > happens to be the target VMA will be the one upon which the merge is > performed which may or may not have VM_SOFTDIRTY set. > > Now we have the concept of 'sticky' VMA flags, let's make VM_SOFTDIRTY one > which solves this issue. > > Additionally update VMA userland tests to propagate changes. > Oh. This patch messes with the comments which mm-implement-sticky-vma-flags-fix-2.patch just altered. Not sure what you intend here, so I left it as below - please advise. (also, I fixed a typo: s/most/must/, both files) --- a/include/linux/mm.h~mm-propagate-vm_softdirty-on-merge +++ a/include/linux/mm.h @@ -532,28 +532,28 @@ extern unsigned int kobjsize(const void * possesses it but the other does not, the merged VMA should nonetheless have * applied to it: * + * VM_SOFTDIRTY - if a VMA is marked soft-dirty, that is has not had its + * references cleared via /proc/$pid/clear_refs, any merged VMA + * should be considered soft-dirty also as it operates at a VMA + * granularity. + * * VM_MAYBE_GUARD - If a VMA may have guard regions in place it implies that * mapped page tables may contain metadata not described by the * VMA and thus any merged VMA may also contain this metadata, * and thus we must make this flag sticky. */ -#define VM_STICKY VM_MAYBE_GUARD +#define VM_STICKY (VM_SOFTDIRTY | VM_MAYBE_GUARD) /* * VMA flags we ignore for the purposes of merge, i.e. one VMA possessing one * of these flags and the other not does not preclude a merge. * - * VM_SOFTDIRTY - Should not prevent from VMA merging, if we match the flags but - * dirty bit -- the caller should mark merged VMA as dirty. If - * dirty bit won't be excluded from comparison, we increase - * pressure on the memory system forcing the kernel to generate - * new VMAs when old one could be extended instead. - * - * VM_STICKY - When merging VMAs, VMA flags must match, unless they are - * 'sticky'. If any sticky flags exist in either VMA, we simply - * set all of them on the merged VMA. + * VM_STICKY - If one VMA has flags which must be 'sticky', that is ones + * which should propagate to all VMAs, but the other does not, + * the merge should still proceed with the merge logic applying + * sticky flags to the final VMA. */ -#define VM_IGNORE_MERGE (VM_SOFTDIRTY | VM_STICKY) +#define VM_IGNORE_MERGE VM_STICKY /* * Flags which should result in page tables being copied on fork. These are --- a/tools/testing/vma/vma_internal.h~mm-propagate-vm_softdirty-on-merge +++ a/tools/testing/vma/vma_internal.h @@ -122,28 +122,23 @@ extern unsigned long dac_mmap_min_addr; * possesses it but the other does not, the merged VMA should nonetheless have * applied to it: * - * VM_MAYBE_GUARD - If a VMA may have guard regions in place it implies that - * mapped page tables may contain metadata not described by the - * VMA and thus any merged VMA may also contain this metadata, - * and thus we must make this flag sticky. + * VM_SOFTDIRTY - if a VMA is marked soft-dirty, that is has not had its + * references cleared via /proc/$pid/clear_refs, any merged VMA + * should be considered soft-dirty also as it operates at a VMA + * granularity. */ -#define VM_STICKY VM_MAYBE_GUARD +#define VM_STICKY (VM_SOFTDIRTY | VM_MAYBE_GUARD) /* * VMA flags we ignore for the purposes of merge, i.e. one VMA possessing one * of these flags and the other not does not preclude a merge. * - * VM_SOFTDIRTY - Should not prevent from VMA merging, if we match the flags but - * dirty bit -- the caller should mark merged VMA as dirty. If - * dirty bit won't be excluded from comparison, we increase - * pressure on the memory system forcing the kernel to generate - * new VMAs when old one could be extended instead. - * - * VM_STICKY - When merging VMAs, VMA flags must match, unless they are - * 'sticky'. If any sticky flags exist in either VMA, we simply - * set all of them on the merged VMA. + * VM_STICKY - If one VMA has flags which most be 'sticky', that is ones + * which should propagate to all VMAs, but the other does not, + * the merge should still proceed with the merge logic applying + * sticky flags to the final VMA. */ -#define VM_IGNORE_MERGE (VM_SOFTDIRTY | VM_STICKY) +#define VM_IGNORE_MERGE VM_STICKY /* * Flags which should result in page tables being copied on fork. These are _