Messages in this thread | | | From | Andy Lutomirski <> | Date | Thu, 8 Aug 2013 17:11:30 -0700 | Subject | Re: [RFC 0/3] Add madvise(..., MADV_WILLWRITE) |
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On Thu, Aug 8, 2013 at 12:25 PM, Andy Lutomirski <luto@amacapital.net> wrote: > > Whoops -- I read your email too quickly. I haven't tried > MADV_WILLNEED, but I think I tried reading each page to fault them in. > Is there any reason to expect MADV_WILLNEED to do any better? I'll > try to do some new tests to see how well this all works. > > (I imagine that freshly fallocated files are somehow different when > read, since there aren't zeros on the disk backing them until they get > written.)
Well, this will teach me to write code based on an old benchmark from memory. It seems that prefaulting for read is okay on Linux 3.9 -- latencytop isn't do_wp_page or ext4* at all, at least not for the last couple minutes on my test box.
I wonder if ext4 changed its handling of fallocated extents somewhere between 3.5 and 3.9. In any case, please consider these patches withdrawn for the time being.
* With file_update_time stubbed out. I need to dust off my old patches to fix that part.
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