Re: Status of buffered write path (deadlock fixes)

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Nick Piggin wrote:
Mark Fasheh wrote:

->commit_write() would probably do fine. Currently, block_prepare_write()
uses it to know which buffers were newly allocated (the file system specific
get_block_t sets the bit after allocation). I think we could safely move
the clearing of that bit to block_commit_write(), thus still allowing us to
detect and zero those blocks in generic_file_buffered_write()


OK, great, I'll make a few patches and see how they look. What did you
think of those other uninitialised buffer problems in my first email?

Hmm, doesn't look like we can do this either because at least GFS2
uses BH_New for its own special things.

Also, I don't know if the trick of only walking over BH_New buffers
will work anyway, since we may still need to release resources on
other buffers as well. As you say, filesystems are simply not set up
to expect this, which is a problem.

Maybe it isn't realistic to change the API this way, no matter how
bad it is presently.

What if we tackle the problem a different way?

1. In the case of no page in the pagecache (or an otherwise
!uptodate page), if the operation is a full-page write then we
first copy all the user data *then* lock the page *then* insert it
into pagecache and go on to call into the filesystem.

2. In the case of a !uptodate page and a partial-page write, then
we can first bring the page uptodate, then continue (goto 3).

3. In the case of an uptodate page, we could perform a full-length
commit_write so long as we didn't expand i_size further than was
copied, and were sure to trim off blocks allocated past that
point.

This scheme IMO is not as "nice" as the partial commit patches,
but in practical terms it may be much more realistic.

--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com -
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]
  Powered by Linux