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 1FB353E6DEC for ; Fri, 4 Sep 2026 16:01:43 +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=1788537704; cv=none; b=TueyDEd+nys1BbfvyATJ2Pscn7DTyNS5hnXM/Pc0LHJzxAu1Y1vH3qWM0jNeQnzQLz+ssqweCqo+JqFQOWSkPL51xQFgHWHElEAYbVjTTioIsfh+ZtBdO1jSys2syRWpVJsY7lxQMvWnRODISGpmzCiOJlo9H/3K/zORK7k3dGU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788537704; c=relaxed/simple; bh=zPud9uRaZUeYLvrNTFZirkjYRt/gCopw3esGeYvILK0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uoURn4xLFOIoF30TRLHJjofDxhxRR+UIM6ma+SBIyiC/C7QEhffhHGEb581yZ7Q6+OVWxLCLY4qieATLyYdbWBOOZPbeuDx2D5kwVTZHgyCfQqEV/137W6FjSYnr3lStCHAlETH89EM2LljL+ZiPcm4IKOE+Q36BNcaFJWptaZM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Chil6rRr; 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="Chil6rRr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8D48F1F00A3D; Fri, 4 Sep 2026 16:01:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788537703; bh=8+ocR7sGCB/9B0UdyCqbIbFztIKXJYrXR0zQcU6I5Pk=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Chil6rRr5FT32LVSVmyd3qa03Z6aWYEodRak43Dgt3mp/StVMgtwJgJen31j+J38z HBqo9q1Pvh2oaYpcONL8zfTAcnHYvTPF0SnAc69CT5/OYBlnIEhj5aCjlnpaPQvLjB dcv36lkfAh39srnfz+qlMNJAPlKIom69Ukx5AF4QwkBFtUNtTYq0k9J2nBJESHMNtg RJ+A1XK/QIuaHPP+DMw4cdQd0pDrXmya7Yg23jvT2fBMtLyK484HXXm0pGQ1QXugN3 eMVhHRqWzRfaIGE9kfcAtgwYRuvTRbuVD/x0MP+gJFe5o8lGC4ZWwvpgdkHH1rcsDz vdWIzqbTzQheg== Date: Fri, 4 Sep 2026 17:01:37 +0100 From: "Lorenzo Stoakes (ARM)" To: Pedro Falcato Cc: Andrew Morton , "Liam R. Howlett" , David Hildenbrand , Vlastimil Babka , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mike Kaplinskiy , zhaozhengzhuo Subject: Re: [PATCH] mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED Message-ID: References: <20260904-madv-will-need-map-private-v1-1-6b83cc99fcff@kernel.org> 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-Disposition: inline In-Reply-To: On Fri, Sep 04, 2026 at 04:24:59PM +0100, Pedro Falcato wrote: > On Fri, Sep 04, 2026 at 04:12:53PM +0100, Lorenzo Stoakes (ARM) wrote: > > Currently MADV_WILLNEED treats file-backed and pure anonymous mappings > > entirely separately - using POSIX_FADV_WILLNEED (equivalent of a readahead) > > for the former and a tree walk and swap in to swap cache for the latter. > > > > MAP_PRIVATE-file backed mappings straddle the two and currently get treated > > as if they were purely file-backed, meaning any swapped out private pages > > remain swapped out. > > > > Resolve the issue by explicitly checking for CoW'd MAP_PRIVATE-file backed > > mappings and performing both walks in this case. > > > > Since the logic checks for vma->anon_vma this means un-CoW'd > > MAP_PRIVATE-file backed mappings retain only the single file walk. > > > > Reported-by: Mike Kaplinskiy > > Closes: https://lore.kernel.org/all/CABeknB_S2XJSHFgnHdgnN0rjzHhH4oQJs_APq9fvxHztQ_pgiA@mail.gmail.com/ > > Signed-off-by: Lorenzo Stoakes (ARM) > > --- > > mm/madvise.c | 6 ++++-- > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > index 73c2901b9adb..d0510dd49dde 100644 > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -297,10 +297,12 @@ static long madvise_willneed(struct madvise_behavior *madv_behavior) > > loff_t offset; > > > > #ifdef CONFIG_SWAP > > - if (!file) { > > + if (!file || (vma_is_cow_mapping(vma) && vma->anon_vma)) { > > Couldn't this all be simplified to > > if (vma->anon_vma) { > > ? swapin needs anon pages to have been faulted-in. Non-cow mappings won't > have an anon_vma, nor will fully empty anonymous VMAs (and that's fine). > Right? Hmm good point :) Though the if (!file) return 0; Would have to be outside of the block to avoid an anon unfaulted (nop) from being skipped. And it's a real improvement to have unfaulted anon skip... But I find that version is documenting what's going on a lot less. Since both anon and MAP_PRIVATE file-backed are CoW mappings we could just reference that. Andrew - could you swap the patch out in-place with below? Thanks! Cheers, Lorenzo ----8<---- >From a706374a1186b6b4409a0e760e8728bcadba0c96 Mon Sep 17 00:00:00 2001 From: "Lorenzo Stoakes (ARM)" Date: Thu, 3 Sep 2026 20:08:39 +0100 Subject: [PATCH] mm/madvise: swap in CoW'd MAP_PRIVATE-file mappings on MADV_WILLNEED Currently MADV_WILLNEED treats file-backed and pure anonymous mappings entirely separately - using POSIX_FADV_WILLNEED (equivalent of a readahead) for the former and a tree walk and swap in to swap cache for the latter. MAP_PRIVATE-file backed mappings straddle the two and currently get treated as if they were purely file-backed, meaning any swapped out private pages remain swapped out. Resolve the issue by explicitly checking for CoW'd MAP_PRIVATE-file backed mappings and performing both walks in this case. Since the logic checks for vma->anon_vma this means un-CoW'd MAP_PRIVATE-file backed mappings retain only the single file walk. Reported-by: Mike Kaplinskiy Closes: https://lore.kernel.org/all/CABeknB_S2XJSHFgnHdgnN0rjzHhH4oQJs_APq9fvxHztQ_pgiA@mail.gmail.com/ Signed-off-by: Lorenzo Stoakes (ARM) --- mm/madvise.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index 73c2901b9adb..963337f93a7a 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -297,11 +297,12 @@ static long madvise_willneed(struct madvise_behavior *madv_behavior) loff_t offset; #ifdef CONFIG_SWAP - if (!file) { + if (vma_is_cow_mapping(vma) && vma->anon_vma) { walk_page_range_vma(vma, start, end, &swapin_walk_ops, vma); lru_add_drain(); /* Push any new pages onto the LRU now */ - return 0; } + if (!file) + return 0; if (shmem_mapping(file->f_mapping)) { shmem_swapin_range(vma, start, end, file->f_mapping); -- 2.55.0