From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomasz Chmielewski Subject: Re: Interesting problem with write data. Date: Thu, 18 Nov 2010 17:00:16 +0100 Message-ID: <4CE54D90.10005@wpkg.org> References: <4CE51613.8060609@wpkg.org> <1290090160-sup-1717@think> <4CE53EDE.0@wpkg.org> <1290092740-sup-9020@think> <4CE54899.9010600@wpkg.org> <1290095654-sup-1115@think> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Cc: linux-btrfs To: Chris Mason Return-path: In-Reply-To: <1290095654-sup-1115@think> List-ID: On 18.11.2010 16:54, Chris Mason wrote: > Excerpts from Tomasz Chmielewski's message of 2010-11-18 10:39:05 -0500: >> On 18.11.2010 16:07, Chris Mason wrote: >> >> (...) >> >>>> [27821.906513] btrfs-cache-8 D ffff88050c5fde98 0 8089 2 0x00000000 >>>> [27821.906517] ffff88051c3a9b60 0000000000000046 ffff88051c3a9b00 ffff88051c3a9fd8 >>>> [27821.906522] 00000000000139c0 00000000000139c0 ffff88051c3a9fd8 ffff88051c3a9fd8 >>>> [27821.906526] 00000000000139c0 ffff88050c5fde98 ffff88050c5fdea0 ffff88050c5fdb00 >>>> [27821.906530] Call Trace: >>>> [27821.906534] [] io_schedule+0x5e/0xa0 >>>> [27821.906538] [] sync_page+0x45/0x60 >>> >>> So, you're caching block groups. What you want to do is use Josef's new >>> block group caching code. >>> >>> mount -o space_cache /dev/xxx >>> >>> Do the test and let the caching threads finish, then unmount and then >>> your next run should be fast. >> >> # mount -o space_cache /dev/sdb4 /mnt/btrfs/ >> [29720.305741] btrfs: enabling disk space caching >> [29720.305743] btrfs: force clearing of disk cache >> >> >> I don't see any difference in behaviour with this mount option; it still >> "hangs" for quite a bit at around ~1.8 GB (and reading with ~500 kB/s >> when the hangs happens) on a subsequent dd run (several runs, >> unmounts/mounts). > > Right, you have to wait for all the caching threads to finish before you > unmount. How do I find out? Is non changing reads/writes enough? # vmstat -p /dev/sdb4 1 sdb4 reads read sectors writes requested writes 185104 1560696 114662 97396104 185104 1560696 114662 97396104 185104 1560696 114662 97396104 185104 1560696 114662 97396104 -- Tomasz Chmielewski http://wpkg.org