Messages in this thread | | | Date | Mon, 6 Apr 2009 23:21:41 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 1/3] block_write_full_page: Use synchronous writes for WBC_SYNC_ALL writebacks |
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On Fri, 27 Mar 2009 16:24:29 -0400 "Theodore Ts'o" <tytso@mit.edu> wrote:
> When doing synchronous writes because wbc->sync_mode is set to > WBC_SYNC_ALL, send the write request using WRITE_SYNC, so that we > don't unduly block system calls such as fsync(). >
Who what where why when? How does this patch work?
> --- > fs/buffer.c | 5 +++-- > 1 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/fs/buffer.c b/fs/buffer.c > index 891e1c7..e7ebd95 100644 > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -1714,6 +1714,7 @@ static int __block_write_full_page(struct inode *inode, struct page *page, > struct buffer_head *bh, *head; > const unsigned blocksize = 1 << inode->i_blkbits; > int nr_underway = 0; > + int write_op = (wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE); > > BUG_ON(!PageLocked(page)); > > @@ -1805,7 +1806,7 @@ static int __block_write_full_page(struct inode *inode, struct page *page, > do { > struct buffer_head *next = bh->b_this_page; > if (buffer_async_write(bh)) { > - submit_bh(WRITE, bh); > + submit_bh(write_op, bh); > nr_underway++; > } > bh = next; > @@ -1859,7 +1860,7 @@ recover: > struct buffer_head *next = bh->b_this_page; > if (buffer_async_write(bh)) { > clear_buffer_dirty(bh); > - submit_bh(WRITE, bh); > + submit_bh(write_op, bh); > nr_underway++; > } > bh = next;
<spends faaaaaaaaaaaaaaaaaaaaaar too long trying to work out what WRITE_SYNC does>
ytf can't we document these things?
I'm having trouble distinguishing all that code from a pile of crap.
I mean, let's graph it:
WRITE_SYNC -> WRITE_SYNC_PLUG -> BIO_RW_SYNCIO -> bio_sync() -> REQ_RW_SYNC -> rw_is_sync() -> does something mysterious in get_request() -> rq_is_sync() -> does something mysterious in IO schedulers -> BIO_RW_NOIDLE -> bio_noidle() -> REQ_NOIDLE -> rq_noidle() -> does something mysterious in cfq-iosched only -> BIO_RW_UNPLUG -> bio_unplug() -> REQ_UNPLUG -> OK, the cognoscenti know what this is supposed to do, but it is unused!
It this really really so obvious and simple that we can afford to leave WRITE_SYNC semantics undocumented?
All this makes it impossible to review your patch.
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