Messages in this thread | | | Subject | Re: [RFC][PATCH] kmap_atomic_push | From | Peter Zijlstra <> | Date | Fri, 09 Oct 2009 00:57:16 +0200 |
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On Thu, 2009-10-08 at 18:27 -0400, jim owens wrote: > So if I understand this correctly, the sequence: > > in = kmap_atomic(inpage, KM_USER1); > > out = kmap_atomic(outpage, KM_USER0); > > kunmap_atomic(in, KM_USER1); > > in = kmap_atomic(next_inpage, KM_USER1); > > is now illegal with this patch, which breaks code > I am testing now for btrfs. > > My code does this because the in/out are zlib inflate > and the in/out run at different rates.
You can do things like:
do { in = kmap_atomic(inpage); out = kmap_atomic(outpage);
<deflate until end of either in/out>
kunmap_atomic(outpage); kunmap_atomic(inpage);
cond_resched();
<iterate bits>
} while (<not done>)
The double unmap gives a preemption point, which sounds like a good thing to have, because your scheme could run for a long while without enabling preemption, which is badness.
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