Andrew Morton wrote:
On Fri, 16 Nov 2007 11:47:27 +0900 Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx> wrote:
Currently fdatasync is identical to fsync in ext3,4.
I think fdatasync should skip journal flush in data=ordered and data=writeback mode
because this syscall is not required to synchronize the metadata.
I suppose so. Although one wonders what earthly point there is in syncing
a file's data if we haven't yet written out the metadata which is required
for locating that data.
IOW, fdatasync() is only useful if the application knows that it is overwriting
already-instantiated blocks.
In which case it might as well have used fsync(). For ext2-style filesystems,
anyway.
hm. It needs some thought.
There are non-trivial amount of performance critical programs,
particularly in financial application segment ported from legacy UNIX
platforms, know the difference between fsync() and fdatasync(). Those
can certainly take advantages of this separation. Don't underestimate
the talents of these application programmers.
-- Wendy
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