Andrew Morton wrote:
Nick Piggin <[email protected]> wrote:
Andrew Morton wrote:
Well, for example you might want to msync a number of disjoint parts of the
mapping, then write them all out in one hit.
That should still be pretty efficient with 2.4 like behaviour?
It's a bit of a disaster if you happen to msync(MS_ASYNC) the same page at
any sort of frequency - we have to wait for the previous I/O to complete
before new I/O can be started. That was the main problem which caused this
change to be made. You can see that it'd make 100x or 1000x speed improvements
with some sane access patterns.
I'm not sure you'd have to do that, would you? Just move the dirty bit
from the pte and skip the page if it is found locked or writeback.
pdflush
does write them out in file offset order doesn't it?
pdflush does, but an msync(MS_ASYNC) which starts I/O puts the IO order
into the application's control.
I don't see a problem with that. There are plenty of ways to shoot oneself
in the foot.
Or you may not actually _want_ to start the I/O now - you just want pdflush
to write things back in a reasonable time period, so you don't have unsynced
data floating about in memory for eight hours. That's a quite reasonable
application of msync(MS_ASYNC).
I think data integrity requirements should be handled by MS_SYNC.
Well that's always been the case. MS_ASYNC doesn't write metadata.
So I don't understand your argument for using MS_ASYNC in that case.
--
SUSE Labs, Novell Inc.
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