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 976193EBF34 for ; Fri, 6 Mar 2026 16:00:07 +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=1772812807; cv=none; b=CV7uwWZh466bgt/9w/8YCydLDxTzmHLXMR5vIzOvlhGdxBwVIiXclm3eliAXbw2bpy/4TmG4lHlsXYj1Oas/8lHL3nxj+LcHbJ4+1coad/RB+mcioPMq2kC+hC+RdQsCr4dSb1xFK29rcrvIsFFPyxiFCARPiZF9VnSuzHJUEoo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772812807; c=relaxed/simple; bh=b454bzPbl55ULZOmmc23V4LQKs1U8z6A+oTB2cMxkSw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OI2PP97G4dLbdEXWz9IYCv/WbVJUjDJ6huGZhh1M59+xnDD+Cc4VZU/hdhPselvCFKClSj798BvmvJ9rK37RKauE0FD/GQki94IJrTeyMx0QJPooOwDgk7x7EF8lbd9fH+kDYhJggqOh0oxF7MINPwJrAZpAqj3zX5etupvdfPo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=j8WNbSnN; 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="j8WNbSnN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 79BB7C4CEF7; Fri, 6 Mar 2026 16:00:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772812807; bh=b454bzPbl55ULZOmmc23V4LQKs1U8z6A+oTB2cMxkSw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=j8WNbSnNmvDwOEQchSrC+awLU1F9TWqkmTuQb3KvRpAWzLZUou3D2zzmuiS70gZst Bwh7Rl9TvfXwyWnldJX5HHuaemXXQi7DRfRcLyJPjVFKnw1+1TlSa2TwmtDO4gC3qZ SsjHQhoYF375E35KJUUMbA3z9iVJvPN1gmhF5c+qtjvl8fDY/ZAsG4pCvqkzZOlwrZ 96lpeY6THs1o2800tnctleliaxJ6DVjEL58BBvLikn6o6CIi0KBcSywr5bhQOmeG6k fANs39ciRtTxyGcNUR7fDgCyNsxmJGtaT5oJWRjq5/I1L9qFqOKV9/oNAUWE9k2uGs OxrKcLaTxIjkg== Message-ID: <546df3d8-2f63-4a83-be44-4cfe21ddb4c6@kernel.org> Date: Fri, 6 Mar 2026 16:59:56 +0100 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 v6 06/13] mm: Add helpers to create migration entries from struct pages To: Jordan Niethe , linux-mm@kvack.org Cc: balbirs@nvidia.com, matthew.brost@intel.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, ziy@nvidia.com, apopple@nvidia.com, lorenzo.stoakes@oracle.com, lyude@redhat.com, dakr@kernel.org, airlied@gmail.com, simona@ffwll.ch, rcampbell@nvidia.com, mpenttil@redhat.com, jgg@nvidia.com, willy@infradead.org, linuxppc-dev@lists.ozlabs.org, intel-xe@lists.freedesktop.org, jgg@ziepe.ca, Felix.Kuehling@amd.com, jhubbard@nvidia.com, maddy@linux.ibm.com, mpe@ellerman.id.au, ying.huang@linux.alibaba.com References: <20260202113642.59295-1-jniethe@nvidia.com> <20260202113642.59295-7-jniethe@nvidia.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 2/2/26 12:36, Jordan Niethe wrote: > To create a new migration entry for a given struct page, that page is > first converted to its pfn, before passing the pfn to > make_readable_migration_entry() (and friends). > > A future change will remove device private pages from the physical > address space. This will mean that device private pages no longer have a > pfn and must be handled separately. > > Prepare for this with a new set of helpers: > > - make_readable_migration_entry_from_page() > - make_readable_exclusive_migration_entry_from_page() > - make_writable_migration_entry_from_page() This is pretty horrible. And everything I see in successive patches around that is not any better. Seriously, look at how terrible make_readable_exclusive_migration_entry_from_page() is. make_readable_exclusive_migration_device_private_entry is not any better, but at least doesn't have this questionable flags parameter. Correct me if I am wrong: all we want is: make_readable_migration_entry() etc. to create something that softleaf_to_page() / softleaf_to_folio() can properly convert to a folio, right? So maybe we should convert make_readable_migration_entry() and friends to consume a page (not add new functions ...), and let it internally figure out how to communicate in the entry that what we are dealing with is not an ordinary pfn, but a special device-private entry. > > Signed-off-by: Jordan Niethe > --- > v1: > - New to series > v2: > - Add flags param > v3: > - No change > v4: > - s/make_writeable_migration_entry_from_page/make_writable_migration_entry_from_page/ > for the !CONFIG_MIGRATION case > --- > include/linux/leafops.h | 14 ++++++++++++++ > include/linux/swapops.h | 34 ++++++++++++++++++++++++++++++++++ > mm/huge_memory.c | 29 +++++++++++++++++------------ > mm/hugetlb.c | 15 +++++++++------ > mm/memory.c | 5 +++-- > mm/migrate_device.c | 12 ++++++------ > mm/mprotect.c | 10 +++++++--- > mm/rmap.c | 12 ++++++------ > 8 files changed, 96 insertions(+), 35 deletions(-) > > diff --git a/include/linux/leafops.h b/include/linux/leafops.h > index a9ff94b744f2..52a1af3eb954 100644 > --- a/include/linux/leafops.h > +++ b/include/linux/leafops.h > @@ -363,6 +363,20 @@ static inline unsigned long softleaf_to_pfn(softleaf_t entry) > return swp_offset(entry) & SWP_PFN_MASK; > } > > +/** > + * softleaf_to_flags() - Obtain flags encoded within leaf entry. > + * @entry: Leaf entry, softleaf_has_pfn(@entry) must return true. > + * > + * Returns: The flags associated with the leaf entry. > + */ > +static inline unsigned long softleaf_to_flags(softleaf_t entry) > +{ > + VM_WARN_ON_ONCE(!softleaf_has_pfn(entry)); > + > + /* Temporary until swp_entry_t eliminated. */ > + return swp_offset(entry) & (SWP_MIG_YOUNG | SWP_MIG_DIRTY); > +} The whole flags stuff does not really belong in this patch. If there are cleanups to be had, perform them separately, please. -- Cheers, David