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Wed, 04 Nov 2026 16:38:34 +0000 X-Mizu-Trace-ID: 8ed0b4cf6e12cb23 X-Migadu-Flow: FLOW_OUT From: Usama Arif To: "Zi Yan" Cc: Usama Arif , "Andrew Morton" , david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, linux-mm@kvack.org, 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, qi.zheng@linux.dev, luizcap@redhat.com, kernel-team@meta.com Subject: Re: [PATCH v8 08/30] mm: recognize PMD swap entries in the softleaf layer Date: Wed, 4 Nov 2026 08:38:29 -0800 Message-ID: <20261104163830.3586103-1-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: References: X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: 3mmw7q8ajafomau5ooxd6zt3cnrwu9ea X-Rspamd-Server: rspam01 X-Rspam-User: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 11848120004 X-HE-Tag: 1793810315-574416 X-HE-Meta: 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 CsuuKfFT bP9bCAfb5iLy+J78YSsrSWomtDt0EuihS9XYKDj1NcL/uj8Kq8c53Dzdrv2vFMeDODMDzD15UxV25aPLrSSjDd78o9LTP3JcN5EILZXxgxvWwt4ilwu+UMRQ6kuVnB4EOPiTITPoJUIUHwMg5dZUp6mpziN69rA351WR6GkFyA/U72AV9SB05g7kCLmBBIA6icNGijdCAwQ7Mxo1Atzrdfl75zl+YTWXBMrcHTCVFyYNKCKIDktS6Opg5wJZp1FuEuV9q9OabepS8+jEhMe7EpKf7Aw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, 07 Oct 2026 22:06:57 -0400 "Zi Yan" wrote: > On Fri Oct 2, 2026 at 5:52 AM EDT, Usama Arif wrote: > > Reclaim splits a PMD-mapped anonymous THP into PTE-level swap entries > > before unmapping it, so an ordinary swap entry has never had to appear in a > > PMD. Prepare for installing one there instead: the softleaf layer is where > > every consumer decodes non-present PMDs. > > > > Accept swap entries as valid PMD softleaves and add pmd_is_swap_entry(). > > A swap entry carries no PFN, so make pmd_softleaf_to_folio() warn and > > return NULL rather than interpret a swap offset as a page frame number. > > > > Unlike migration and device-private entries, a PMD swap entry can also > > carry the swap-exclusive marker, which softleaf_from_pmd() has to strip > > before decoding. Strip all three overlays unconditionally while we are > > here: each clear is a plain bit clear, so testing first only buys a branch. > > > > Signed-off-by: Usama Arif > > Acked-by: David Hildenbrand (Arm) > > Reviewed-by: Kiryl Shutsemau (Meta) > > --- > > include/linux/leafops.h | 40 ++++++++++++++++++++++++++++------------ > > include/linux/pgtable.h | 17 +++++++++++++++++ > > 2 files changed, 45 insertions(+), 12 deletions(-) > > > > diff --git a/include/linux/leafops.h b/include/linux/leafops.h > > index 7c13c58a5e218..ce176c78cefd4 100644 > > --- a/include/linux/leafops.h > > +++ b/include/linux/leafops.h > > @@ -98,10 +98,9 @@ static inline softleaf_t softleaf_from_pmd(pmd_t pmd) > > if (pmd_present(pmd) || pmd_none(pmd)) > > return softleaf_mk_none(); > > > > - if (pmd_swp_soft_dirty(pmd)) > > - pmd = pmd_swp_clear_soft_dirty(pmd); > > - if (pmd_swp_uffd(pmd)) > > - pmd = pmd_swp_clear_uffd(pmd); > > + pmd = pmd_swp_clear_soft_dirty(pmd); > > + pmd = pmd_swp_clear_uffd(pmd); > > + pmd = pmd_swp_clear_exclusive(pmd); > > I notice there is pte_swp_clear_flags() and wonder if we want > pmd_swp_clear_flags() to match it. Added pmd_swp_clear_flags() alongside pte_swp_clear_flags() and used it in softleaf_from_pmd() for the next revision. > > > arch_entry = __pmd_to_swp_entry(pmd); > > > > /* Temporary until swp_entry_t eliminated. */ > > @@ -634,18 +633,29 @@ 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. */ > > return softleaf_is_device_private(entry) || > > - softleaf_is_migration(entry); > > + softleaf_is_migration(entry) || > > + softleaf_is_swap(entry); > > Using softleaf_is_swap() here makes softleaf_is_valid_pmd_entry() return > false positive when pmd swap entry is not possible at the moment. Adding > it only after pmd swap entry is possible can close the gap. But the > whole series should be applied together, so it should be fine. > > Otherwise, LGTM. > The predicate accepts the new encoding before the producer is enabled, but no PMD swap entry can be installed at that point. Reclaim still uses TTU_SPLIT_HUGE_PMD until the final swap-out patch. I kept the ordering so each consumer is ready before entries can be produced. As you said, there is no reachable intermediate PMD swap entry to mishandle. > Reviewed-by: Zi Yan > Thanks for the reviews! > -- > Best Regards, > Yan, Zi > >