Messages in this thread | | | Date | Thu, 7 Feb 2019 10:41:38 +0100 | From | Andre Noll <> | Subject | Re: bcache on XFS: metadata I/O (dirent I/O?) not getting cached at all? |
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On Thu, Feb 07, 16:16, Coly Li wrote > From: Coly Li <colyli@suse.de> > Date: Thu, 7 Feb 2019 15:54:24 +0800 > Subject: [PATCH] bcache: use (REQ_META|REQ_PRIO) to indicate bio for metadata > > In 'commit 752f66a75aba ("bcache: use REQ_PRIO to indicate bio for > metadata")' REQ_META is replaced by REQ_PRIO to indicate metadata bio. > This assumption is not always correct, e.g. XFS uses REQ_META to mark > metadata bio other than REQ_PRIO. This is why Nix reports a regression > that bcache does not cache metadata for XFS after the above commit.
maybe s/reports a regression/noticed
> Thanks to Dave Chinner, he explains the difference between REQ_META and > REQ_PRIO from view of file system developer. Here I quote part of his > explanation from mailing list, > REQ_META is used for metadata. REQ_PRIO is used to communicate to > the lower layers that the submitter considers this IO to be more > important that non REQ_PRIO IO and so dispatch should be expedited. > > IOWs, if the filesystem considers metadata IO to be more important > that user data IO, then it will use REQ_PRIO | REQ_META rather than > just REQ_META. > > Then it seems bios with REQ_META or REQ_PRIO should both be cached for > performance optimation, because they are all probably low I/O latency > demand by upper layer (e.g. file system). > > So in this patch, when we want to check whether a bio is metadata > related, REQ_META and REQ_PRIO are both checked. Then both metadata and > high priority I/O requests will be handled properly.
s/check whether a bio is metadata related/decide whether to bypass the cache
Apart from these two nitpicks, feel free to add my Reviewed-by.
Thanks Andre -- Max Planck Institute for Developmental Biology Max-Planck-Ring 5, 72076 Tübingen, Germany. Phone: (+49) 7071 601 829 http://people.tuebingen.mpg.de/maan/ [unhandled content-type:application/pgp-signature] | |