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From: Muchun Song In-Reply-To: <04f5b50a-a526-4644-b9f0-c54a0d6db702@linux.dev> Date: Tue, 14 Jul 2026 19:22:39 +0800 Cc: linux-arch@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, apopple@nvidia.com, arnd@arndb.de, balbirs@nvidia.com, bp@alien8.de, dave.hansen@linux.intel.com, david@kernel.org, kees@kernel.org, mingo@redhat.com, rppt@kernel.org, tglx@kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <67BC9BE5-A201-4DED-B847-8C74BF30B16D@linux.dev> References: <20260709112520.24857-1-lizhe.67@bytedance.com> <20260709112520.24857-9-lizhe.67@bytedance.com> <04f5b50a-a526-4644-b9f0-c54a0d6db702@linux.dev> To: Li Zhe X-Migadu-Flow: FLOW_OUT X-Stat-Signature: nr69z8b9cnj4ocur56shf69n7xepkmt5 X-Rspamd-Queue-Id: D1A58160002 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1784028209-828570 X-HE-Meta: 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 U2LN9Nuy UKAtmr97HtrxnpLuweLmVFIX1G0uRGkmcv/4WogEXrrXy9/32rXxGUf79w/1uk0F0OZbdS8JaUxNP2HqCUJttqY7lSTgh63FQj6IjwgcunhQK645VaJDRyHQDBJyF8ZbEAxjHMrz9xfK1y0+xxcM7W7GM6sWz0Ci1GPtwyGm7sM4IGL2YiRm6vLv80N1XT2TgqjzKFfOIz8SKajg6uS5Ryu8GG8ST48Gpezg0jBzDZzlH/0vc4BfLUl579d7w3LIJELgS14m8hqtDfIkQmatvmrWqlNU9vVfII90hPy5FxiBgMmVbrw8qT0GRkfGtewwFJmO1164R4rR8G+1EvaXyqnjHyPFlQCpYRrh/ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Jul 14, 2026, at 17:45, Muchun Song wrote: >=20 >=20 >=20 > On 2026/7/9 19:25, Li Zhe wrote: >> The template fast path currently uses memcpy() for the actual struct >> page copy. Switch zone_device_page_init_from_template() to = memcpy_nt() >> and add memcpy_nt_drain() before memmap_init_compound(), before >> prep_compound_head() updates overlapping tail metadata, and before >> returning from memmap_init_zone_device(). >>=20 >> ZONE_DEVICE memmap initialization is largely write-once: each struct >> page is populated once, and most destination cachelines are not = expected >> to be reused immediately afterwards. On x86, a regular cached = memcpy() >> can therefore incur write-allocate traffic by pulling destination >> cachelines into the cache before writeback, and can populate the = cache >> with data that has little near-term reuse. Using memcpy_nt() lets = this >> path request non-temporal stores for that copy pattern, which can = reduce >> cache pollution and avoid part of the associated write-allocate >> overhead, while architectures without a specialized backend still = fall >> back to memcpy(). >>=20 >> When memcpy_nt() maps to non-temporal stores, order those stores = before >> memmap_init_compound(), before prep_compound_head() updates = overlapping >> compound metadata, and before returning from = memmap_init_zone_device(). >>=20 >> Keep sanitized builds on the slow path so KASAN/KMSAN retain their >> instrumented stores. >>=20 >> Tested in a VM with a 100 GB fsdax namespace device configured with >> map=3Ddev and a 100 GB devdax namespace (align=3D2097152) on Intel = Ice Lake >> server. >>=20 >> Test procedure: >> Rebind the nd_pmem and dax_pmem driver 30 times and collect the = memmap >> initialization time from the pr_debug() output of >> memmap_init_zone_device(). >>=20 >> Base(v7.2-rc1): >> First binding for nd_pmem driver: 1456 ms >> Average of subsequent rebinds: 244.28 ms >>=20 >> First binding for dax_pmem driver: 1462 ms >> Average of subsequent rebinds: 273.31 ms >>=20 >> With this series: >> First binding for nd_pmem driver: 1272 ms >> Average of subsequent rebinds: 96.79 ms >>=20 >> First binding for dax_pmem driver: 1354 ms >> Average of subsequent rebinds: 119.04 ms >>=20 >> This reduces the average rebind time by about 60.4% for nd_pmem and >> 56.4% for dax_pmem. >>=20 >> Signed-off-by: Li Zhe >> --- >> mm/mm_init.c | 39 +++++++++++++++++++++++++++++++++++++-- >> 1 file changed, 37 insertions(+), 2 deletions(-) >>=20 >> diff --git a/mm/mm_init.c b/mm/mm_init.c >> index fb855bb0437a..addb4969587e 100644 >> --- a/mm/mm_init.c >> +++ b/mm/mm_init.c >> @@ -1067,11 +1067,21 @@ static void __ref = zone_device_page_init_slow(struct page *page, >>=20 >> static inline bool zone_device_page_init_optimization_enabled(void) >> { >> + /* >> + * Keep sanitized builds on the slow path so their stores stay >> + * instrumented. >> + */ >> + if (IS_ENABLED(CONFIG_KASAN) || IS_ENABLED(CONFIG_KMSAN)) >> + return false; >=20 > It is not a major concern if struct page initialization lacks KASAN or > KMSAN instrumentation. To keep things simple, let's just entirely = remove > zone_device_page_init_optimization_enabled() to simplify the code. BTW, If you really want to properly support KASAN, you should integrate the check directly into memcpy_flushcache() via kasan_check_write(), = rather than treating it as a special case here. >=20 > Thanks. >=20 >> + >> /* >> * The template fast path copies a preinitialized struct page image. >> * Skip it when the page_ref_set tracepoint is enabled. >> */ >> - return !page_ref_tracepoint_active(page_ref_set); >> + if (page_ref_tracepoint_active(page_ref_set)) >> + return false; >> + >> + return true; >> } >>=20 >> static inline void zone_device_tail_page_init(struct page *page, >> @@ -1110,7 +1120,7 @@ static void = zone_device_page_init_from_template(struct page *page, >> * to the destination page. >> */ >> zone_device_page_update_template(template, pfn); >> - memcpy(page, template, sizeof(*page)); >> + memcpy_nt(page, template, sizeof(*page)); >> } >>=20 >> /* >> @@ -1179,6 +1189,15 @@ static void __ref memmap_init_compound(struct = page *head, >> &template); >> } >> } >> + >> + /* >> + * When the template path is enabled, order the preceding tail-page = copies >> + * before prep_compound_head() updates the overlapping compound = metadata >> + * in the first tail-page descriptors. If memcpy_nt() fell back to >> + * regular cached stores, memcpy_nt_drain() may be a no-op. >> + */ >> + if (use_template) >> + memcpy_nt_drain(); >> prep_compound_head(head, order); >> } >>=20 >> @@ -1238,10 +1257,26 @@ void __ref memmap_init_zone_device(struct = zone *zone, >> if (pfns_per_compound =3D=3D 1) >> continue; >>=20 >> + /* >> + * When the template path is enabled, order the preceding head-page = copy >> + * before memmap_init_compound(), which immediately updates = compound-head >> + * metadata. If memcpy_nt() fell back to regular cached stores, >> + * memcpy_nt_drain() may be a no-op. >> + */ >> + if (use_template) >> + memcpy_nt_drain(); >> + >> memmap_init_compound(page, pfn, zone_idx, nid, pgmap, >> compound_nr_pages(pfn, altmap, pgmap), >> use_template); >> } >> + /* >> + * Ensure any prior template copies are ordered before returning. >> + * On architectures where memcpy_nt() used regular cached stores, >> + * memcpy_nt_drain() may be a no-op. >> + */ >> + if (use_template) >> + memcpy_nt_drain(); >>=20 >> pageblock_migratetype_init_range(start_pfn, nr_pages, = MIGRATE_MOVABLE); >>=20 >> -- >> 2.20.1 >>=20 >=20