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b=K/c2SWuZ5zJkEu+Y1yk5X0LsveGqtcKkrhA9l+sgGx+tiv42m6esO0dkJ8qFqmFTD X4MQfQVy/hdSAmOaqW63/bfRNEgegrDpg0zkJiVVN8yZOp2PhQZDd8Luj+I9Zc0ogR qxz+Q+E6gmwFtzcJ1J/oVmXxXYWiMckPSZJ6M1uB+UvcMoaOL+FYR2jZJPahKDHrBO Z8/aE2ke7Fl9Gm/J4bMqaVhZ32CeFP0HcSpTKHpCpB4b+s/Qk71VRwepcP/rjbGoll IjWVevtZnjioMr4o5uIY7cA6ud4lb7BqRAmMq4iY7w8En+YkgHcwZOF1IXy4GF3ALx 95sNL0Zu1y0qQ== Message-ID: Date: Thu, 18 Dec 2025 08:49:41 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 8/8] mm: folio_zero_user: cache neighbouring pages To: Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org Cc: akpm@linux-foundation.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, mjguzik@gmail.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, willy@infradead.org, raghavendra.kt@amd.com, chleroy@kernel.org, ioworker0@gmail.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com References: <20251215204922.475324-1-ankur.a.arora@oracle.com> <20251215204922.475324-9-ankur.a.arora@oracle.com> From: "David Hildenbrand (Red Hat)" Content-Language: en-US In-Reply-To: <20251215204922.475324-9-ankur.a.arora@oracle.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: bugpkqeki3uox5fn3xjfmh85bst6ytyf X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 431F0C0009 X-HE-Tag: 1766044190-582925 X-HE-Meta: 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 iUndIjJh fdrRgV2Z9Q9WYj7iOw6GAFjtUfOVoMx/tf+r18aoaVYiZGEzVqmpqGuQVrfWY/oHVHCrQEvTDfo+k/MpSFli8aps/BiMs+ckUCz0IP2wpKoxhfinG5qOr/rq9WCvsxHT5UdCm92c2RqPtjuXy/7TiuRtZORX69/eI3iTz8Z97/ude3XpfR0f4L6YgJryZO20J9H3tJTTpBb7SnW99qdaTJEASXxFn2ZXuldyGyIFZ/BUkNuS/DJzqREgje0xJBeQhDexDJwtOu9j1JFE9rx4GmCLBs481YI5YfnvUamjBSUUvoSDQEW/jaBFBYSyxgoKLJ3Ly1zacz81HkC2hGhZZdz6jybkp4r9NJU8C 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 12/15/25 21:49, Ankur Arora wrote: > folio_zero_user() does straight zeroing without caring about > temporal locality for caches. > > This replaced commit c6ddfb6c5890 ("mm, clear_huge_page: move order > algorithm into a separate function") where we cleared a page at a > time converging to the faulting page from the left and the right. > > To retain limited temporal locality, split the clearing in three > parts: the faulting page and its immediate neighbourhood, and, the > remaining regions on the left and the right. The local neighbourhood > will be cleared last. > Do this only when zeroing small folios (< MAX_ORDER_NR_PAGES) since > there isn't much expectation of cache locality for large folios. > > Performance > === > > AMD Genoa (EPYC 9J14, cpus=2 sockets * 96 cores * 2 threads, > memory=2.2 TB, L1d= 16K/thread, L2=512K/thread, L3=2MB/thread) > > anon-w-seq (vm-scalability): > stime utime > > page-at-a-time 1654.63 ( +- 3.84% ) 811.00 ( +- 3.84% ) > contiguous clearing 1602.86 ( +- 3.00% ) 970.75 ( +- 4.68% ) > neighbourhood-last 1630.32 ( +- 2.73% ) 886.37 ( +- 5.19% ) > > Both stime and utime respond in expected ways. stime drops for both > contiguous clearing (-3.14%) and neighbourhood-last (-1.46%) > approaches. However, utime increases for both contiguous clearing > (+19.7%) and neighbourhood-last (+9.28%). > > In part this is because anon-w-seq runs with 384 processes zeroing > anonymously mapped memory which they then access sequentially. As > such this is likely an uncommon pattern where the memory bandwidth > is saturated while also being cache limited because we access the > entire region. > > Kernel make workload (make -j 12 bzImage): > > stime utime > > page-at-a-time 138.16 ( +- 0.31% ) 1015.11 ( +- 0.05% ) > contiguous clearing 133.42 ( +- 0.90% ) 1013.49 ( +- 0.05% ) > neighbourhood-last 131.20 ( +- 0.76% ) 1011.36 ( +- 0.07% ) > > For make the utime stays relatively flat with an up to 4.9% improvement > in the stime. Nice evaluation! > > Signed-off-by: Ankur Arora > Reviewed-by: Raghavendra K T > Tested-by: Raghavendra K T > --- > mm/memory.c | 44 ++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 42 insertions(+), 2 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 974c48db6089..d22348b95227 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -7268,13 +7268,53 @@ static void clear_contig_highpages(struct page *page, unsigned long addr, > * @addr_hint: The address accessed by the user or the base address. > * > * Uses architectural support to clear page ranges. > + * > + * Clearing of small folios (< MAX_ORDER_NR_PAGES) is split in three parts: > + * pages in the immediate locality of the faulting page, and its left, right > + * regions; the local neighbourhood is cleared last in order to keep cache > + * lines of the faulting region hot. > + * > + * For larger folios we assume that there is no expectation of cache locality > + * and just do a straight zero. Just wondering: why not do the same thing here as well? Probably shouldn't hurt and would get rid of some code? > */ > void folio_zero_user(struct folio *folio, unsigned long addr_hint) > { > unsigned long base_addr = ALIGN_DOWN(addr_hint, folio_size(folio)); While at it you could turn that const as well. > + const long fault_idx = (addr_hint - base_addr) / PAGE_SIZE; > + const struct range pg = DEFINE_RANGE(0, folio_nr_pages(folio) - 1); > + const int width = 2; /* number of pages cleared last on either side */ Is "width" really the right terminology? (the way you describe it, it's more like diameter?) Wondering whether we should turn that into a define to make it clearer that we are dealing with a magic value. Speaking of magic values, why 2 and not 3? :) > + struct range r[3]; > + int i; > > - clear_contig_highpages(folio_page(folio, 0), > - base_addr, folio_nr_pages(folio)); > + if (folio_nr_pages(folio) > MAX_ORDER_NR_PAGES) { > + clear_contig_highpages(folio_page(folio, 0), > + base_addr, folio_nr_pages(folio)); > + return; > + } > + > + /* > + * Faulting page and its immediate neighbourhood. Cleared at the end to > + * ensure it sticks around in the cache. > + */ > + r[2] = DEFINE_RANGE(clamp_t(s64, fault_idx - width, pg.start, pg.end), > + clamp_t(s64, fault_idx + width, pg.start, pg.end)); > + > + /* Region to the left of the fault */ > + r[1] = DEFINE_RANGE(pg.start, > + clamp_t(s64, r[2].start-1, pg.start-1, r[2].start)); "start-1" -> "start - 1" etc. > + > + /* Region to the right of the fault: always valid for the common fault_idx=0 case. */ > + r[0] = DEFINE_RANGE(clamp_t(s64, r[2].end+1, r[2].end, pg.end+1), > + pg.end); Same here. > + > + for (i = 0; i <= 2; i++) { Can we use ARRAY_SIZE instead of "2" ? > + unsigned int npages = range_len(&r[i]); > + struct page *page = folio_page(folio, r[i].start); > + unsigned long addr = base_addr + folio_page_idx(folio, page) * PAGE_SIZE; Can't you compute that from r[i].start) instead? The folio_page_idx() seems avoidable unless I am missing something. Could make npages and addr const. const unsigned long addr = base_addr + r[i].start * PAGE_SIZE; const unsigned int npages = range_len(&r[i]); struct page *page = folio_page(folio, r[i].start); > + > + if (npages > 0) > + clear_contig_highpages(page, addr, npages); > + } > } > > static int copy_user_gigantic_page(struct folio *dst, struct folio *src, -- Cheers David