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([43.153.32.141]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-269803184d3sm7860915ad.116.2025.09.17.18.31.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Sep 2025 18:31:32 -0700 (PDT) From: Jinliang Zheng X-Google-Original-From: Jinliang Zheng To: harry.yoo@oracle.com Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, alexjlzheng@gmail.com, alexjlzheng@tencent.com, arnd@arndb.de, bp@alien8.de, dave.hansen@linux.intel.com, david@redhat.com, geert@linux-m68k.org, hpa@zytor.com, joro@8bytes.org, jroedel@suse.de, kas@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux@armlinux.org.uk, lorenzo.stoakes@oracle.com, mhocko@suse.com, mingo@redhat.com, rppt@kernel.org, surenb@google.com, tglx@linutronix.de, thuth@redhat.com, urezki@gmail.com, vbabka@suse.cz, vincenzo.frascino@arm.com, x86@kernel.org Subject: Re: [PATCH] mm: introduce ARCH_PAGE_TABLE_SYNC_MASK_VMALLOC to sync kernel mapping conditionally Date: Thu, 18 Sep 2025 09:31:30 +0800 Message-ID: <20250918013130.2425537-1-alexjlzheng@tencent.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: AFF50140007 X-Stat-Signature: sc7eydpetpunxjifn53if7jbhpjyqxji X-Rspam-User: X-HE-Tag: 1758159094-397270 X-HE-Meta: U2FsdGVkX1/jEocgQOeZhwTN6LeGcfXUCV3Jn++GQh2THUvUaw6dChLXN98b6lMYUt8hYU8mkAERwv9xzQJG6FXxFobIclQAGBDtweKSfIS4FXiqBJmCL33xBgAsgQHBaZOiOx+NePnl3oHJV8Nr+v2sR4YLJloK9/8VmxiotaQ8kp0zWzhULw/cOpLLBeL1IsmBriehpkE/d9MLpLnzpe3+ksrMUjMl340baJQN+LthqCO2duwLcD+qciQzWNXi4EKDYohxClQkPOQHtfpOaVmPW+M8wy8SSrng+YykceUQT0IzFPc6OtIXM7dyPfXONB6r9hNDRs4hVWVlorwGBvy1V5dgHKdAYhj+QNK+LZOShdz9pLzDxC0NjJxqeuupbTZmn3GotTMG8k2BNGSzg14jiMvloM9/agfVJ2UtDIRvfFtDTeBt0vwaqhH2PYQegvF7/C/cevm8EhQw0X4844cSBCAUptCTsi9vzpCASHLLDKUtaTDnYHedHTALIxs7osfy+to3ZRzV1ET8iGFI+7JJHMxT2wtLmkPhVF4uT1PKIUvd0rJIbIGKHKm8HaHGoCLsKgNXE2IAbWDL6lV37OrTyd5LmzjhdptopKlt/sY9h4pCAcbPxtNEWNUPYSI0MxJ+d/Svj6jOnEsQI33Q9FKc0Xl1Y527rokw1jmor17AtDKcqlXy6S1737q/zdujUdLrdkTO1y1heOQArRv360JjMquKsmKMxpqQa40dOfvh9qshUV5dedy5hVagAfgRv7IUVwOL+QTd1czDmjPnZDfidWPCZU0VUGfzzI1I/LhFqL4CkL8xR19BPB2+ukbQwzEKJ30Vkjw1HtCjOWc+ePlO5uyhvXPQfzajS+pXUUd7VRY+7ny+g3hVk0kxSTtAVmb0cNRWMSOmjTOTuSsjVJQk5pG7Pp0EGmneHquGn6WI7eKZboT4WZjvnNVgUZk1zrC5+5gvKWISatMpKZS 9u4jvvP5 ib43jAILSiRPMpEId91ke7i0w3J5qKPj3C8ar4KJINiByi7wU1Dx6sJpVB67J+6lYL/tQOnW21Plijs8VGIK2cdf5ft+5FsGu/HPAgwQ9tW6PyqQpAkK4bg+PN0FvWNvzs8sjcpkg9Vcn+jt48LXnV8qntc98jg0PBkPtr1t4iE3lJrHl4vbW2obC1lM0YDEDEBGfaLqxYNQubaLcKbK8skG0/3tpNVwtzMTlwAs4YIHKXqTvqQn7ImeTzRDUoz8ATWTjkqt4pOHJIHWcVgrJY4qPrio65rz8pb85uJJc1ZKE6RzKSZdtrHuv1UA5JsEC5jgbSHEIU8bXxuiA527GSVcHpncLhSEUSUQmr0dwD7NRJu21KoYofLT8W60UIWTk/GgNS4RcTK04pLpE5bruwWwxR+R3TmrwiBbGThT8MBzjNvvbaAq7QbahGiiGJeXwMK/8/Bw7VqhI1z8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 18 Sep 2025 01:41:04 +0900, harry.yoo@oracle.com wrote: > On Wed, Sep 17, 2025 at 11:48:29PM +0800, alexjlzheng@gmail.com wrote: > > From: Jinliang Zheng > > > > After commit 6eb82f994026 ("x86/mm: Pre-allocate P4D/PUD pages for > > vmalloc area"), we don't need to synchronize kernel mappings in the > > vmalloc area on x86_64. > > Right. > > > And commit 58a18fe95e83 ("x86/mm/64: Do not sync vmalloc/ioremap > > mappings") actually does this. > > Right. > > > But commit 6659d0279980 ("x86/mm/64: define ARCH_PAGE_TABLE_SYNC_MASK > > and arch_sync_kernel_mappings()") breaks this. > > Good point. > > > This patch introduces ARCH_PAGE_TABLE_SYNC_MASK_VMALLOC to avoid > > unnecessary kernel mappings synchronization of the vmalloc area. > > > > Fixes: 6659d0279980 ("x86/mm/64: define ARCH_PAGE_TABLE_SYNC_MASK and arch_sync_kernel_mappings()") > > The commit is getting backported to -stable kernels. > > Do you think this can cause a visible performance regression from > user point of view, or it's just a nice optimization to have? > (and any data to support?) Haha, when I woke up in bed this morning, I suddenly realized that I might have pushed a worthless patch and wasted everyone's precious time. Sorry for that. :-( After commit 6eb82f994026 ("x86/mm: Pre-allocate P4D/PUD pages for vmalloc area"), pgd_alloc_track()/p4d_alloc_track() in vmalloc() and apply_to_range() may should always return a mask that does not contain PGTBL_PGD_MODIFIED (5 level pgtable) or PGTBL_P4D_MODIFIED (4 level pgtable), thereby bypassing the call to arch_sync_kernel_mappings(). Right? thanks, Jinliang Zheng. :) > > > Signed-off-by: Jinliang Zheng > > --- > > arch/arm/include/asm/page.h | 3 ++- > > arch/x86/include/asm/pgtable-2level_types.h | 3 ++- > > arch/x86/include/asm/pgtable-3level_types.h | 3 ++- > > include/linux/pgtable.h | 4 ++++ > > mm/memory.c | 2 +- > > mm/vmalloc.c | 6 +++--- > > 6 files changed, 14 insertions(+), 7 deletions(-) > > > > diff --git a/mm/memory.c b/mm/memory.c > > index 0ba4f6b71847..cd2488043f8f 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -3170,7 +3170,7 @@ static int __apply_to_page_range(struct mm_struct *mm, unsigned long addr, > > break; > > } while (pgd++, addr = next, addr != end); > > > > - if (mask & ARCH_PAGE_TABLE_SYNC_MASK) > > + if (mask & ARCH_PAGE_TABLE_SYNC_MASK_VMALLOC) > > arch_sync_kernel_mappings(start, start + size); > > But vmalloc is not the only user of apply_to_page_range()? > > -- > Cheers, > Harry / Hyeonggon