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Re: sync writes - was Re: how to counteract slowdown



On Wednesday November 14, akpm zip com au wrote:
> Neil Brown wrote:
> > 
> > ButButButButButBut
> 
> Sorry.  I misread your script.
> 
> It would appear to be an outrageous bug.  Linux isn't
> syncing write() data for either synchronous mounts or
> for `chattr +S' files.
> 
> Here's a fix.  It could adversely affect ext3 - I'll check.
> 

Thanks. 
I applied your fix (the version you sent to linux-kernel actually) and
re-ran my test.
The results look more like what I expected, with one exception.
With ext3 -o data=writeback, fsync does not cause any writes to the
filesystem.  This means that either the data is being written to the
journal, which I doubt, or that ext3  does *not* sync data in response
to fsync when using data=writeback.

NeilBrown

Output from patched 2.4.15-pre4

ext2 sync
     async       101    0
     fsync       200    0
     osync       100    0
ext2 async
     async         0    0
     fsync       200    0
     osync       101    0
ext3 sync,data=journal
     async         0  200
     fsync         0  300
     osync         0  200
ext3 async,data=journal
     async         0    0
     fsync         0  200
     osync         0  200
ext3 sync,data=ordered
     async       100  200
     fsync       100  300
     osync       100  200
ext3 async,data=ordered
     async         0    0
     fsync       100  200
     osync       100  200
ext3 sync,data=writeback
     async       100  200
     fsync       100  300
     osync       100  200
ext3 async,data=writeback
     async         0    0
     fsync         0  200  <---- This one is odd.
     osync       100  200





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