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Sun, 01 Nov 2026 06:59:37 +0000 X-Mizu-Trace-ID: 3eacaad6ebce6e07 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Sun, 1 Nov 2026 14:59:29 +0800 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 02/12] mm: hugetlb_vmemmap: unify VMEMMAP_{SPLIT,REMAP}_NO_TLB_FLUSH To: Muchun Song Cc: Muchun Song , Oscar Salvador , Andrew Morton , Mike Rapoport , Lance Yang , James Houghton , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261020115306.813483-1-songmuchun@bytedance.com> <20261020115824.823278-1-songmuchun@bytedance.com> <86d9a986-58ea-44f5-a8af-514abff12c2a@linux.dev> <99503D05-0C4D-45E4-B5D6-EDD927838935@linux.dev> From: Qi Zheng In-Reply-To: <99503D05-0C4D-45E4-B5D6-EDD927838935@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 46A16A0003 X-Spam-Status: No, score=-17.3 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_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: g89ay5g8wgwxfcxscja694t8aiodacri X-HE-Tag: 1793516379-388135 X-HE-Meta: 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 HimqrFRX LfQH4pTOWRQpqUhKrsFVzk0CzSmRJgtu4vrByr7MZikZq69S2iQ5Qpb0HcIcMm/4CegWumQ3H/7wrBeGTuD8FhkDRLQLmH7kv9/7T3OYynF2XeqXYfcnxOlQfNkTM5ireQJPZzmYoZ1NbqxEUME97ZQO8uvK6Uu5SbnTi4g/IxCKcW0ZgUq3TsDJF/ycoon8YA/eeqyf6et/zTE1+W/fO63bA3VkiCLbgSsK84tyhthKQXCocVb28ks6r9SKXoEQ+HACHzCf/IZeAIJIDjSwWIkVlf8Bv2Hf/QauMspcndoooDa/T1hWWH7UaFabJQIaGM/q+IXiXYCRdvx7UXDebNvuECw== 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 11/1/26 2:56 PM, Muchun Song wrote: > > >> On Nov 1, 2026, at 14:22, Qi Zheng wrote: >> >> >> >> On 10/20/26 7:58 PM, Muchun Song wrote: >>> VMEMMAP_SPLIT_NO_TLB_FLUSH and VMEMMAP_REMAP_NO_TLB_FLUSH do not >>> describe fully independent choices. A split-only walk can defer the >>> PMD-split flush to a later global flush, and a remap-only walk can >>> defer the final remap flush. However, when a PMD split is followed >>> by PTE remapping, the split flush must happen before the PTEs are >>> changed, because stale large-page translations must not overlap with >>> new small-page translations that map different physical pages. >>> Replace the two flags with a single VMEMMAP_REMAP_NO_TLB_FLUSH flag. >>> Keep split-only walks able to defer the flush, but force the split >>> flush whenever a remap_pte callback is present. Callers that batch >>> HVO work can still defer the final remap flush and issue their own >>> global flush. >>> Current callers keep the same flushing behavior. >>> Signed-off-by: Muchun Song >>> --- >>> mm/hugetlb_vmemmap.c | 15 +++++++++------ >>> 1 file changed, 9 insertions(+), 6 deletions(-) >>> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c >>> index 1105aa925acc..8b3abb562599 100644 >>> --- a/mm/hugetlb_vmemmap.c >>> +++ b/mm/hugetlb_vmemmap.c >>> @@ -42,10 +42,8 @@ struct vmemmap_remap_walk { >>> struct list_head *vmemmap_pages; >>> -/* Skip the TLB flush when we split the PMD */ >>> -#define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0) >>> -/* Skip the TLB flush when we remap the PTE */ >>> -#define VMEMMAP_REMAP_NO_TLB_FLUSH BIT(1) >>> +/* Skip the TLB flush while updating the vmemmap page tables. */ >>> +#define VMEMMAP_REMAP_NO_TLB_FLUSH BIT(0) >> >> Since this flag is now also used by the split-only path, the >> VMEMMAP_REMAP_NO_TLB_FLUSH name is somewhat misleading. Moreover, the >> flag does not suppress every TLB flush, as the PMD-split flush is still >> mandatory when remapping follows. > > Yeah, good point. > >> >> Would VMEMMAP_DEFER_TLB_FLUSH better describe its semantics? It > > I think so. > >> indicates that flushes which can be safely batched are deferred, without >> implying that all TLB flushes are skipped. > > I'll change it along side with the comment to: > > /* Defer safely batchable TLB flushes to the caller. */ > #define VMEMMAP_DEFER_TLB_FLUSH BIT(0) LGTM, with this change: Reviewed-by: Qi Zheng Thanks, Qi