Messages in this thread | | | Date | Thu, 1 Apr 2004 17:19:49 +0100 | From | Jamie Lokier <> | Subject | Re: msync() behaviour broken for MS_ASYNC, revert patch? |
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Stephen C. Tweedie wrote: > Yes, but we _used_ to have that choice --- call msync() with flags == 0, > and you'd get the deferred kupdated writeback;
Is that not equivalent to MS_INVALIDATE? It seems to be equivalent in 2.6.4.
The code in 2.6.4 ignores MS_INVALIDATE except for trivial error checks, so msync() with flags == MS_INVALIDATE has the same effect as msync() with flags == 0.
Some documentation I'm looking at says MS_INVALIDATE updates the mapped page to contain the current contents of the file. 2.6.4 seems to do the reverse: update the file to contain the current content of the mapped page. "man msync" agrees with the the latter. (I can't look at SUS right now).
On systems where the CPU caches are fully coherent, the only difference is that the former is a no-op and the latter does the same as the new behaviour of MS_ASYNC.
On systems where the CPU caches aren't coherent, some cache synchronising or flushing operations are implied.
On either type of system, MS_INVALIDATE doesn't seem to be doing what the documentation I'm looking at says it should do.
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