Re: bad lmbench numbers for mmap
V Ganesh (ganesh@vxindia.veritas.com)
Sat, 17 Apr 1999 07:09:03 +0530 (IST)
> > From: Jakub Jelinek <jj@sunsite.mff.cuni.cz>
> Date: Sat, 17 Apr 1999 01:03:21 +0200 (CEST)
>
> > > so what's up with mmap ?
>
> Actually it seems like more than 90% of the time in this test is spent in
> munmap, particularly in filemap_sync. From quick looking at the sources, the
> only routine which changed there substantially is filemap_write_page, so it
> might well be because it waits for every dirtied page until it is stored to
> disk and in 2.1.103 did not do that. I'm too tired now to investigate
> further and actually think about it whether doing so is needed.
not very likely. if you are writing out a swap page, filemap_write_page
queues the request to kpiod, which seems to be the only new feature in there.
otherwise it just winds up calling ext2_file_write which doesn't normally
wait for all pages to hit disk.
ganesh
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