Re: Request: I/O request recording

From: Andrew Morton (akpm_at_osdl.org)
Date: 01/26/04

  • Next message: Andrew Morton: "Re: [2.6 patch] show "Fusion MPT device support" menu only if BLK_DEV_SD" 
    Date:	Sun, 25 Jan 2004 15:09:14 -0800
To: Bart Samwel <bart@samwel.tk>

    Bart Samwel <bart@samwel.tk> wrote:
    >
    > When I saw this thread I've fiddled for a bit with the block_dump
    > functionality that's in the laptop_mode patch. I wanted to see if it
    > could support a similar thing completely from user space (except for the
    > block_dump code, of course). I've written a small tool to generate a
    > complete file that lists tuples (sector, size, device) from the kernel
    > output in syslog; it parses all "READ block xxx" messages since the
    > last reboot. Putting this through sort -n -u delivers a nicely sorted
    > file, ready for optimized reading.
    >
    > Unfortunately I'm now stuck within the other part, which is reading the
    > pages back in memory at the next boot. It's not working, and I was
    > hoping someone here could take a look and tell me what I'm doing wrong.

    Linux caches disk data on a per-file basis. So if you preload pagecache
    via the /dev/hda1 "file", that is of no benefit to the /etc/passwd file.
    Each one has its own unique pagecache. When reading pages for /etc/passwd
    we don't go looking for the same disk blocks in the cache of /dev/hda1.

    Which is why the userspace cache preloading needs to know the pathnames of
    all the relevant files - it needs to open and read each one, applying
    knowledge of disk layout while doing it.

    -
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