Re: [PATCH 002 of 8] md/bitmap: Remove bitmap writeback daemon.

[Andrew Morton <akpm@osdl.org>]

NeilBrown <neilb@suse.de> wrote:
>
>  ./drivers/md/bitmap.c         |  115 ++----------------------------------------

hmm.  I hope we're not doing any of that filesystem I/O within the context
of submit_bio() or kblockd or anything like that.  Looks OK from a quick
scan.

a_ops->commit_write() already ran set_page_dirty(), so you don't need that
in there.

I assume this always works in units of a complete page?  It's strange to do
prepare_write() followed immediately by commit_write().  Normally
prepare_write() will do some prereading, but it's smart enough to not do
that if the caller is preparing to write the whole page.

We normally use PAGE_CACHE_SIZE for these things, not PAGE_SIZE.  Same diff.

If you have a page and you want to write the whole thing out then there's
really no need to run prepare_write or commit_write at all.  Just
initialise the whole page, run set_page_dirty() then write_one_page().

Perhaps it should check that the backing filesystem actually implements
commit_write(), prepare_write(), readpage(), etc.  Some might not, and the
user will get taught not to do that via an oops.