From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-220.mta1.migadu.com [95.215.58.220]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 64D994A32 for ; Wed, 19 Aug 2026 12:31:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.220 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787142681; cv=none; b=Y4JZYxhAkK+VY0mcs2kuSKjl5p4TVMv72rhtrCnPVgSNaHFzmSKW/Rw199jzWfSmbGN9C9z69GAS10Bq95pp6lWw809DzPYTJujWfBRHSC5N6m7mIAR3ASHKzBqrjt8n8o6djhRSSCydeU0TdFlFtUubMtmU3zVCTy2C6YEK4Jw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787142681; c=relaxed/simple; bh=/otDFlr1rhHbSmXliBx4mVZMc6saGUTu0UfzxL4rnTc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LqdkwQZ4/GgB5Se8TmS74VzAe/w8eMLk3yjhUdO9eUnnNBUCZ7w+nheuudv2i0pU38S8msS0zUvOWLRcDoHug/yMlIC9axh+hNu0Ph4bh/LyPxw7SG1uvdG4bQKf4i1Alyu0GHbbFmzVcuopvh2iSXKDN3UmNR9QdEOXZ6M2TEw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=b8RM31S+; arc=none smtp.client-ip=95.215.58.220 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="b8RM31S+" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=/otDFlr1rhHbSmXliBx4mVZMc6saGUTu0UfzxL4rnTc=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787142677; v=1; x=1787747477; b=b8RM31S+GrsFhcDwEhFpTN7iMKzN1WcQtXiXHa2RtwNLYSWzi4TmVPP/O77Ei47Cz7yMiUi/ 9tRk0N7dpCb0qHV6ed6QLDmPwr6mSAqfktUxe/MgGJ7en71hf59LuzUx+/Mv8J7JpGZ01YJPdhx atgFRntPIm4RM+fV2EtQu3bA= X-Envelope-To: linux-kernel@vger.kernel.org Received: from [IPV6:2a03:83e0:1126:4:9d:a05e:5bd8:c200] (2620:10d:c092:500::4:a428) by smtp.migadu.com with ESMTPS id 24c9a4ea09970955; Wed, 19 Aug 2026 12:31:17 +0000 X-Migadu-Flow: FLOW_OUT Message-ID: <5baead5e-b9e9-4850-9ce3-e48a2e5db2ca@linux.dev> Date: Wed, 19 Aug 2026 13:31:08 +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 02/12] mm: add PMD swap entry detection support To: "David Hildenbrand (Arm)" , Andrew Morton , chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com, linux-mm@kvack.org Cc: ying.huang@linux.alibaba.com, Baoquan He , willy@infradead.org, youngjun.park@lge.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, alex@ghiti.fr, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, Nico Pache , "Liam R. Howlett" , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, kernel-team@meta.com References: <20260818131202.494754-1-usama.arif@linux.dev> <20260818131202.494754-3-usama.arif@linux.dev> <69e8469c-aa7f-4141-be3c-796c9cf11f2f@kernel.org> Content-Language: en-US From: Usama Arif In-Reply-To: <69e8469c-aa7f-4141-be3c-796c9cf11f2f@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 18/08/2026 15:40, David Hildenbrand (Arm) wrote: > On 8/18/26 15:09, Usama Arif wrote: >> Currently when a PMD-mapped THP is swapped out, the PMD is always >> split into HPAGE_PMD_NR PTE-level swap entries. To preserve huge >> page information across swap cycles, later patches will install a >> single PMD-level swap entry instead. Add the infrastructure to detect >> those entries. >> >> Teach the softleaf layer to recognise PMD swap entries: >> pmd_is_swap_entry() detects them and softleaf_is_valid_pmd_entry() >> accepts them as a valid non-present type. Because swap entries do not >> encode a PFN, make pmd_softleaf_to_folio() warn and return NULL for them >> instead of passing the swap offset to softleaf_to_folio(). Clear the >> exclusive overlay bit in softleaf_from_pmd() before decoding, matching >> how soft_dirty and uffd bits are already stripped. >> >> Add pmd_swp_mkexclusive(), pmd_swp_exclusive(), and >> pmd_swp_clear_exclusive() helpers to each architecture that supports >> PMD softleaf entries (x86, arm64, s390, riscv, loongarch, powerpc), >> mirroring the existing PTE swap exclusive helpers in each arch's >> pgtable.h. > > Ah, for migration entries we still use a dedicated migratetype. I actually have > on my todo list to move to PTE bits as well. > > (likely the _swp_ part should then be renamed to indicate that this is for > softdirty entries, not just swap entries) > Agreed. I kept the pmd_swp_* spelling to mirror the existing pte_swp_* API. Renaming the broader softleaf API is independent of this series. Maybe I can add it as a followup? >> Provide generic no-op PMD swap exclusive fallbacks for >> architectures without PMD softleaf support, matching the generic PMD >> swap soft-dirty fallbacks. > > No softleaf implies to migration and no swap, so this would work. > > You should extend mm/debug_vm_pgtable.c in a separate commit to test what > pte_swap_exclusive_tests() tests for PMDs. > I have added this in my series, and will include it in the next revision, Thanks! >> >> Signed-off-by: Usama Arif >> --- >> arch/arm64/include/asm/pgtable.h | 6 +++++ >> arch/loongarch/include/asm/pgtable.h | 19 ++++++++++++++ >> arch/powerpc/include/asm/book3s/64/pgtable.h | 17 +++++++++++++ >> arch/riscv/include/asm/pgtable.h | 15 +++++++++++ >> arch/s390/include/asm/pgtable.h | 17 +++++++++++++ >> arch/x86/include/asm/pgtable.h | 17 +++++++++++++ > > I'm sorry for asking you to compete with Kiryll's series by creating one patch > for each architecture that directly jumps at arch maintainers :) > I have now split the architecture helpers into separate patches, followed by generic support for the next revision. I think I will need split patch 7 and patch 12 into several independent patches as well? This will significantly grow the patch count which is what I was trying to avoid as I feel that makes it more daunting to review (atleast for me), but I will try and keep it under 57 patches to not beat Kiryl :) > [...] > >> #ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY >> static inline pte_t pte_swp_mksoft_dirty(pte_t pte) >> { >> diff --git a/include/linux/leafops.h b/include/linux/leafops.h >> index 7c13c58a5e218..4a6c52974b305 100644 >> --- a/include/linux/leafops.h >> +++ b/include/linux/leafops.h >> @@ -102,6 +102,8 @@ static inline softleaf_t softleaf_from_pmd(pmd_t pmd) >> pmd = pmd_swp_clear_soft_dirty(pmd); >> if (pmd_swp_uffd(pmd)) >> pmd = pmd_swp_clear_uffd(pmd); >> + if (pmd_swp_exclusive(pmd)) >> + pmd = pmd_swp_clear_exclusive(pmd); > > Can't we just unconditionally clear these flags? > > pmd = pmd_swp_clear_uffd(pmd); > pmd = pmd_swp_clear_exclusive(pmd); > > Avoids these rather unnecessary conditionals unless I am missing something. > Yes, we can, will do in next revision. > >> arch_entry = __pmd_to_swp_entry(pmd); >> >> /* Temporary until swp_entry_t eliminated. */ >> @@ -634,18 +636,30 @@ static inline bool pmd_is_migration_entry(pmd_t pmd) >> */ >> static inline bool softleaf_is_valid_pmd_entry(softleaf_t entry) >> { >> - /* Only device private, migration entries valid for PMD. */ >> + /* Device private, migration, and swap entries valid for PMD. */ > > Can we just drop that comment? I mean, it's as clear as it gets in the code > immediately below :) > Will do in next revision. Thanks for the reviews! >> return softleaf_is_device_private(entry) || >> - softleaf_is_migration(entry); >> + softleaf_is_migration(entry) || >> + softleaf_is_swap(entry); >> +} >> + >