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Howlett" , Lorenzo Stoakes Cc: Jann Horn , Thorsten Leemhuis , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Petr Tesarik , Michael Matz , Gabriel Krisman Bertazi , Matthias Bodenbinder , stable@vger.kernel.org, Rik van Riel References: <2050f0d4-57b0-481d-bab8-05e8d48fed0c@leemhuis.info> <20241024151228.101841-2-vbabka@suse.cz> Content-Language: en-US From: Yang Shi In-Reply-To: <20241024151228.101841-2-vbabka@suse.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: CH3P221CA0030.NAMP221.PROD.OUTLOOK.COM (2603:10b6:610:1e7::31) To CH0PR01MB6873.prod.exchangelabs.com (2603:10b6:610:112::22) Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH0PR01MB6873:EE_|DM4PR01MB7884:EE_ X-MS-Office365-Filtering-Correlation-Id: 6cf4b5f7-8f10-4118-f596-08dcf45a4ab8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|366016|1800799024; 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[1] reports regressions in various spec benchmarks, with > up to 600% slowdown of the cactusBSSN benchmark on some platforms. The > benchmark seems to create many mappings of 4632kB, which would have > merged to a large THP-backed area before commit efa7df3e3bb5 and now > they are fragmented to multiple areas each aligned to PMD boundary with > gaps between. The regression then seems to be caused mainly due to the > benchmark's memory access pattern suffering from TLB or cache aliasing > due to the aligned boundaries of the individual areas. > > Another known regression bisected to commit efa7df3e3bb5 is darktable > [2] [3] and early testing suggests this patch fixes the regression there > as well. > > To fix the regression but still try to benefit from THP-friendly > anonymous mapping alignment, add a condition that the size of the > mapping must be a multiple of PMD size instead of at least PMD size. In > case of many odd-sized mapping like the cactusBSSN creates, those will > stop being aligned and with gaps between, and instead naturally merge > again. Thanks for debugging this. The fix makes sense to me. Reviewed-by: Yang Shi > > Reported-by: Michael Matz > Debugged-by: Gabriel Krisman Bertazi > Closes: https://bugzilla.suse.com/show_bug.cgi?id=1229012 [1] > Reported-by: Matthias Bodenbinder > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219366 [2] > Closes: https://lore.kernel.org/all/2050f0d4-57b0-481d-bab8-05e8d48fed0c@leemhuis.info/ [3] > Fixes: efa7df3e3bb5 ("mm: align larger anonymous mappings on THP boundaries") > Cc: > Cc: Rik van Riel > Cc: Yang Shi > Signed-off-by: Vlastimil Babka > --- > mm/mmap.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 9c0fb43064b5..a5297cfb1dfc 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -900,7 +900,8 @@ __get_unmapped_area(struct file *file, unsigned long addr, unsigned long len, > > if (get_area) { > addr = get_area(file, addr, len, pgoff, flags); > - } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { > + } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) > + && IS_ALIGNED(len, PMD_SIZE)) { > /* Ensures that larger anonymous mappings are THP aligned. */ > addr = thp_get_unmapped_area_vmflags(file, addr, len, > pgoff, flags, vm_flags);