[PATCH 0/2 v4] Writeback livelock avoidance for data integrity writes

Jan Kara
2010-06-17T09:12:22Z

Sorry for replying to my email but I forgot to set a subject while doing
git send-email. So at least set it now.

Honza

On Wed 16-06-10 18:33:49, Jan Kara wrote:
> Hello,
>
> here is the fourth version of the writeback livelock avoidance patches
> for data integrity writes. To quickly summarize the idea: we tag dirty
> pages at the beginning of write_cache_pages with a new TOWRITE tag and
> then write only tagged pages to avoid parallel writers to livelock us.
> See changelogs of the patches for more details.
> I have tested the patches with fsx and a test program I wrote which
> checks that if we crash after fsync, the data is indeed on disk.
> If there are no more concerns, can these patches get merged?
>
> Honza
>
> Changes since last version:
> - tagging function was changed to stop after given amount of pages to
> avoid keeping tree_lock and irqs disabled for too long
> - changed names and updated comments as Andrew suggested
> - measured memory impact and reported it in the changelog
>
> Things suggested but not changed (I want to avoid going in circles ;):
> - use tagging also for WB_SYNC_NONE writeback - there's problem with an
> interaction with wbc->nr_to_write. If we tag all dirty pages, we can
> spend too much time tagging when we write only a few pages in the end
> because of nr_to_write. If we tag only say nr_to_write pages, we may
> not have enough pages tagged because some pages are written out by
> someone else and so we would have to restart and tagging would become
> essentially useless. So my option is - switch to tagging for WB_SYNC_NONE
> writeback if we can get rid of nr_to_write. But that's a story for
> a different patch set.
> - implement function for clearing several tags (TOWRITE, DIRTY) at once
> - IMHO not worth it because we would save only conversion of page index
> to radix tree offsets. The rest would have to be separate anyways. And
> the interface would be incosistent as well...
> - use __lookup_tag to implement radix_tree_range_tag_if_tagged - doesn't
> quite work because __lookup_tag returns only leaf nodes so we'd have to
> implement tree traversal anyways to tag also internal nodes.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR