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[80.230.25.21]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48a4b329542sm227417095e9.3.2026.04.21.15.01.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Apr 2026 15:01:24 -0700 (PDT) Date: Tue, 21 Apr 2026 18:01:22 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Andrew Morton , David Hildenbrand , Vlastimil Babka , Brendan Jackman , Michal Hocko , Suren Baghdasaryan , Jason Wang , Andrea Arcangeli , Gregory Price , linux-mm@kvack.org, virtualization@lists.linux.dev, Johannes Weiner , Zi Yan Subject: [PATCH RFC v3 04/19] mm: use folio_zero_user for user pages in post_alloc_hook Message-ID: References: MIME-Version: 1.0 In-Reply-To: X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: yKx6QG_gGVvG3IGjIzzHDtTQ_SN91lRoApstCzoYT3c_1776808887 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Stat-Signature: 33xt7fep7o6adxf4itrtzkr8rrhai14r X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: B743DC0002 X-Rspam-User: X-HE-Tag: 1776808890-548649 X-HE-Meta: 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 w4VxSEEI mDbsENDlx+SmMy1u/c6GftCNowawHOjf6X01HUozm5HIRHrUxBA6Bl1p83yMBrPvvhPSZANE/fJ8zgXKFNAJUbnuBAui8JCVo4RwGNoLYDZVZjJWnh6M+4AXC/ZDlI0UxsfqXfp7n4RA5i2hldbmgCO8dPefBPA7Boyx4yt9YHeTVwghFsyvFN21cyKWAChoOCN2xEb9pmivC9K4YatpSZYFyRKYxYqmWNGtNZXWSmayhNyVorMJcdGJxZp9vxPC1SBVaFBWLF/wVEDaXKvChpgS4I404/LAcFswCrGTPBuNQzRHBtPzqnaQjMUV5mziVL/8p4359+xq6OfTbJmVYwzEvdjrEAu8dsRDbNXCDurNSCV8oTNGNWFI4Hg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: When post_alloc_hook() needs to zero a page for an explicit __GFP_ZERO allocation and user_addr is set, use folio_zero_user() instead of kernel_init_pages(). This zeros near the faulting address last, keeping those cachelines hot for the impending user access. folio_zero_user() is only used for explicit __GFP_ZERO, not for init_on_alloc. On architectures with virtually-indexed caches (e.g., ARM), clear_user_highpage() performs per-line cache operations; using it for init_on_alloc would add overhead that kernel_init_pages() avoids (the page fault path flushes the cache at PTE installation time regardless). No functional change yet: current callers do not pass __GFP_ZERO for user pages (they zero at the callsite instead). Subsequent patches will convert them. Signed-off-by: Michael S. Tsirkin Assisted-by: Claude:claude-opus-4-6 --- mm/page_alloc.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 99c01eb2d59e..db2192ffc27c 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1882,9 +1882,20 @@ inline void post_alloc_hook(struct page *page, unsigned int order, for (i = 0; i != 1 << order; ++i) page_kasan_tag_reset(page + i); } - /* If memory is still not initialized, initialize it now. */ - if (init) - kernel_init_pages(page, 1 << order); + /* + * If memory is still not initialized, initialize it now. + * When __GFP_ZERO was explicitly requested and user_addr is set, + * use folio_zero_user() which zeros near the faulting address + * last, keeping those cachelines hot. For init_on_alloc, use + * kernel_init_pages() to avoid unnecessary cache flush overhead + * on architectures with virtually-indexed caches. + */ + if (init) { + if ((gfp_flags & __GFP_ZERO) && user_addr != USER_ADDR_NONE) + folio_zero_user(page_folio(page), user_addr); + else + kernel_init_pages(page, 1 << order); + } set_page_owner(page, order, gfp_flags); page_table_check_alloc(page, order); -- MST