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  1. 10 8月, 2009 8 次提交
    • P
      NFS: read-modify-write page updating · 38c73044
      由 Peter Staubach 提交于 
      Hi.

I have a proposal for possibly resolving this issue.

I believe that this situation occurs due to the way that the
Linux NFS client handles writes which modify partial pages.

The Linux NFS client handles partial page modifications by
allocating a page from the page cache, copying the data from
the user level into the page, and then keeping track of the
offset and length of the modified portions of the page.  The
page is not marked as up to date because there are portions
of the page which do not contain valid file contents.

When a read call comes in for a portion of the page, the
contents of the page must be read in the from the server.
However, since the page may already contain some modified
data, that modified data must be written to the server
before the file contents can be read back in the from server.
And, since the writing and reading can not be done atomically,
the data must be written and committed to stable storage on
the server for safety purposes.  This means either a
FILE_SYNC WRITE or a UNSTABLE WRITE followed by a COMMIT.
This has been discussed at length previously.

This algorithm could be described as modify-write-read.  It
is most efficient when the application only updates pages
and does not read them.

My proposed solution is to add a heuristic to decide whether
to do this modify-write-read algorithm or switch to a read-
modify-write algorithm when initially allocating the page
in the write system call path.  The heuristic uses the modes
that the file was opened with, the offset in the page to
read from, and the size of the region to read.

If the file was opened for reading in addition to writing
and the page would not be filled completely with data from
the user level, then read in the old contents of the page
and mark it as Uptodate before copying in the new data.  If
the page would be completely filled with data from the user
level, then there would be no reason to read in the old
contents because they would just be copied over.

This would optimize for applications which randomly access
and update portions of files.  The linkage editor for the
C compiler is an example of such a thing.

I tested the attached patch by using rpmbuild to build the
current Fedora rawhide kernel.  The kernel without the
patch generated about 269,500 WRITE requests.  The modified
kernel containing the patch generated about 261,000 WRITE
requests.  Thus, about 8,500 fewer WRITE requests were
generated.  I suspect that many of these additional
WRITE requests were probably FILE_SYNC requests to WRITE
a single page, but I didn't test this theory.

The difference between this patch and the previous one was
to remove the unneeded PageDirty() test.  I then retested to
ensure that the resulting system continued to behave as
desired.

	Thanx...

		ps
Signed-off-by: NPeter Staubach <staubach@redhat.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
      38c73044
    • T
      NFS: Add a ->migratepage() aop for NFS · 074cc1de
      由 Trond Myklebust 提交于 
      Make NFS a bit more friendly to NUMA and memory hot removal...
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
      074cc1de
    • T
      NFSv4: Clean up the nfs.callback_tcpport option · c140aa91
      由 Trond Myklebust 提交于 
      Tighten up the validity checking in param_set_port: check for NULL pointers.
Ensure that the option shows up on 'modinfo' output.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
      c140aa91
    • T
      SUNRPC: convert some sysctls into module parameters · cbf11071
      由 Trond Myklebust 提交于 
      Parameters like the minimum reserved port, and the number of slot entries
should really be module parameters rather than sysctls.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
      cbf11071
    • T
      NFSv4: Don't do idmapper upcalls for asynchronous RPC calls · 80e52ace
      由 Trond Myklebust 提交于 
      We don't want to cause rpciod to hang...
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
      80e52ace
    • T
      NFSv4: Add 'server capability' flags for NFSv4 recommended attributes · 62ab460c
      由 Trond Myklebust 提交于 
      If the NFSv4 server doesn't support a POSIX attribute, the generic NFS code
needs to know that, so that it don't keep trying to poll for it.

However, by the same count, if the NFSv4 server does support that
attribute, then we should ensure that the inode metadata is appropriately
labelled as being untrusted. For instance, if we don't know the correct
value of the file's uid, we should certainly not be caching ACLs or ACCESS
results.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
      62ab460c
    • T
      NFSv4: Don't loop forever on state recovery failure... · a78cb57a
      由 Trond Myklebust 提交于 
      If the server is broken, then retrying forever won't fix it. We
should just give up after a while, and return an error to the user.
We set the number of retries to 10 for now...
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
      a78cb57a
    • R
      nfs: Keep index within mnt_errtbl[] · dd8ac1da
      由 Roel Kluin 提交于 
      Ensure that index i remains within array mnt_errtbl[] and mnt3_errtbl[].
Signed-off-by: NRoel Kluin <roel.kluin@gmail.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>
      dd8ac1da
  3. 08 8月, 2009 32 次提交