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authorVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>2019-10-11 12:07:10 +0300
committerMax Reitz <mreitz@redhat.com>2019-10-28 11:22:30 +0100
commitdbdf699cad505be6ba2d4c93066f1dd7aff15aeb (patch)
treec0ead0f13536d74857401ce49dbe8ee5b05a07da /.mailmap
parentb30168647fea0fc173a0e244d2943fc5575ca511 (diff)
block/mirror: support unaligned write in active mirror
Prior 9adc1cb49af8d do_sync_target_write had a bug: it reset aligned-up region in the dirty bitmap, which means that we may not copy some bytes and assume them copied, which actually leads to producing corrupted target. So 9adc1cb49af8d forced dirty bitmap granularity to be request_alignment for mirror-top filter, so we are not working with unaligned requests. However forcing large alignment obviously decreases performance of unaligned requests. This commit provides another solution for the problem: if unaligned padding is already dirty, we can safely ignore it, as 1. It's dirty, it will be copied by mirror_iteration anyway 2. It's dirty, so skipping it now we don't increase dirtiness of the bitmap and therefore don't damage "synchronicity" of the write-blocking mirror. If unaligned padding is not dirty, we just write it, no reason to touch dirty bitmap if we succeed (on failure we'll set the whole region ofcourse, but we loss "synchronicity" on failure anyway). Note: we need to disable dirty_bitmap, otherwise we will not be able to see in do_sync_target_write bitmap state before current operation. We may of course check dirty bitmap before the operation in bdrv_mirror_top_do_write and remember it, but we don't need active dirty bitmap for write-blocking mirror anyway. New code-path is unused until the following commit reverts 9adc1cb49af8d. Suggested-by: Denis V. Lunev <den@openvz.org> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-id: 20191011090711.19940-5-vsementsov@virtuozzo.com Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
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