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SN7PR12MB8171.namprd12.prod.outlook.com (2603:10b6:806:322::9) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8207.18; Tue, 3 Dec 2024 05:01:57 +0000 Received: from IA1PR12MB6434.namprd12.prod.outlook.com ([fe80::dbf7:e40c:4ae9:8134]) by IA1PR12MB6434.namprd12.prod.outlook.com ([fe80::dbf7:e40c:4ae9:8134%4]) with mapi id 15.20.8207.010; Tue, 3 Dec 2024 05:01:57 +0000 Message-ID: Date: Tue, 3 Dec 2024 10:31:48 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/1] Large folios in block buffered IO path To: Mateusz Guzik Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, nikunj@amd.com, willy@infradead.org, vbabka@suse.cz, david@redhat.com, akpm@linux-foundation.org, yuzhao@google.com, axboe@kernel.dk, viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, joshdon@google.com, clm@meta.com References: <20241127054737.33351-1-bharata@amd.com> 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1733202104-341035 X-HE-Meta: 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lbQLWXP/10vus/XITz3T8KHpTkvELg9I6ce/H/gg1BRE5HoHMSUcKJl7UfPKGxbxnL8n5V1jxjhGWo1ICHLlvv71DotuQHr6s5f0d/y9/+DqLDLv3q2A8N1tu6szAgbjBM5ip3XSgYDFlotvRZ+BDZePcw5uMr8mUC+LIXnAwKNoSM+GVr9hwh+YPUDwFDSdCGue14PlFApmt4Eg3J4gE5LCqHZFpnzrxgWpR57xnxgnN/LuW8iqK1YV4UZWm+LbUAXAETfwnz9pe7w10sWjYlDApGR3yYezq5eUJrbEmi3LBQfjIZZAH0YFXOY7cYoQy6XPaXEfZcspeMMhVfpIadrg24dMdT5ChiVEPGeD8PzEmzSwJXhDs4tCPxsUKU3oe3gSN9hJRQA4iPCDt3mMk0xf3tw== 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 02-Dec-24 3:38 PM, Mateusz Guzik wrote: > On Mon, Dec 2, 2024 at 10:37 AM Bharata B Rao wrote: >> >> On 28-Nov-24 10:01 AM, Mateusz Guzik wrote: >> >>> WIlly mentioned the folio wait queue hash table could be grown, you >>> can find it in mm/filemap.c: >>> 1062 #define PAGE_WAIT_TABLE_BITS 8 >>> 1063 #define PAGE_WAIT_TABLE_SIZE (1 << PAGE_WAIT_TABLE_BITS) >>> 1064 static wait_queue_head_t folio_wait_table[PAGE_WAIT_TABLE_SIZE] >>> __cacheline_aligned; >>> 1065 >>> 1066 static wait_queue_head_t *folio_waitqueue(struct folio *folio) >>> 1067 { >>> 1068 │ return &folio_wait_table[hash_ptr(folio, PAGE_WAIT_TABLE_BITS)]; >>> 1069 } >>> >>> Can you collect off cpu time? offcputime-bpfcc -K > /tmp/out >> >> Flamegraph for "perf record --off-cpu -F 99 -a -g --all-kernel >> --kernel-callchains -- sleep 120" is attached. >> >> Off-cpu samples were collected for 120s at around 45th minute run of the >> FIO benchmark that actually runs for 1hr. This run was with kernel that >> had your inode_lock fix but no changes to PAGE_WAIT_TABLE_BITS. >> >> Hopefully this captures the representative sample of the scalability >> issue with folio lock. Here is the data from offcputime-bpfcc -K run with inode_lock fix and no change to PAGE_WAIT_TABLE_BITS. This data was captured for the entire duration of FIO run (1hr). Since the data is huge, I am pasting a few relevant entries. The first entry in the offcputime records finish_task_switch.isra.0 schedule irqentry_exit_to_user_mode irqentry_exit sysvec_reschedule_ipi asm_sysvec_reschedule_ipi - fio (33790) 2 There are thousands of entries for read and write paths of FIO and I have shown only the first and last entries for the same here. First entry for FIO read path that waits on folio_lock finish_task_switch.isra.0 schedule io_schedule folio_wait_bit_common filemap_get_pages filemap_read blkdev_read_iter vfs_read ksys_read __x64_sys_read x64_sys_call do_syscall_64 entry_SYSCALL_64_after_hwframe - fio (34143) 3381769535 Last entry for FIO read path that waits on folio_lock finish_task_switch.isra.0 schedule io_schedule folio_wait_bit_common filemap_get_pages filemap_read blkdev_read_iter vfs_read ksys_read __x64_sys_read x64_sys_call do_syscall_64 entry_SYSCALL_64_after_hwframe - fio (34171) 3516224519 First entry for FIO write path that waits on folio_lock finish_task_switch.isra.0 schedule io_schedule folio_wait_bit_common __filemap_get_folio iomap_get_folio iomap_write_begin iomap_file_buffered_write blkdev_write_iter vfs_write ksys_write __x64_sys_write x64_sys_call do_syscall_64 entry_SYSCALL_64_after_hwframe - fio (33842) 48900 Last entry for FIO write path that waits on folio_lock finish_task_switch.isra.0 schedule io_schedule folio_wait_bit_common __filemap_get_folio iomap_get_folio iomap_write_begin iomap_file_buffered_write blkdev_write_iter vfs_write ksys_write __x64_sys_write x64_sys_call do_syscall_64 entry_SYSCALL_64_after_hwframe - fio (34187) 1815993 The last entry in the offcputime records finish_task_switch.isra.0 schedule futex_wait_queue __futex_wait futex_wait do_futex __x64_sys_futex x64_sys_call do_syscall_64 entry_SYSCALL_64_after_hwframe - multipathd (6308) 3698877753 Regards, Bharata.