Re: [PATCH] [RFC] gfs2: add flag REQ_PRIO for metadata read ahead

[Bob Peterson <rpeterso@redhat.com>]

----- Original Message -----
| >> This patch adds REQ_PRIO flag when submitting a metadata readahead bio.
| >> A meta data read ahead bio may come from I/O requests for bitmap,
| >> directoriesmeta or other general metadata request.
| >>
| > 
| > Are there any places in gfs2 where REQ_PRIO should be placed on
| > latency-sensitive metadata writes?  They would then writeback in bcache
| > after the relevant bcache patch is merged.
| 
| Hi Eric,
| 
| I just grep REQ_META in fs/gfs2, there are 10 locations use REQ_META.
| Among the 10 locations, REQ_PRIO shows up at 3 locations, another 3
| locations are REQ_READAHEAD and I add REQ_PRIO to them, the rested
| locations are,
| 
| 1) log.c:662
|    In log_write_header(), used to flush gfs2 log header. The author does
| not add REQ_PRIO on purpose, because I see REQ_FUA is there. And for no
| barrier condition, REQ_PRIO is added with REQ_FUA removed. So it's well
| done here.
| 
| 2) meta_io.c:455
|    Here gfs2_meta_ra() tries to read first metadata block, cache the
| metadata block in bcache should be helpful.
| 
| 3) ops_fstype.c:250
|    This is for gfs2_read_sb(), it is only called once by init_sb(), we
| don't need to cache this block by bcache.
| 
| 4) quota.c:733
|    This is in gfs2_write_buf_to_page() when gfs2 disk quota is updated,
| we can have it in cache device.
| 
| So it seems REQ_PRIO might be added at meta_io.c:455, and quota.c:733 to
| provide more hint to bcache.
| 
| Thanks for suggestion.
| 
| Coly

Hi Coly,

So does this mean you are revising the patch and I should wait for a new one?
Or is this patch good as it is? BTW, you may want to change
the comment from "directoriesmeta" to "directory meta".

Regards,

Bob Peterson
Red Hat File Systems