[lkml]   [2002]   [Mar]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: 2.4.19pre1aa1
    On Tue, Mar 05, 2002 at 11:12:46AM -0800, Andrew Morton wrote:
    > Arjan van de Ven wrote:
    > >
    > > On Tue, Mar 05, 2002 at 07:26:04PM +0100, Andrea Arcangeli wrote:
    > >
    > > > Another approch would be to add the pages backing the bh into the lru
    > > > too, but then we'd need to mess with the slab and new bitflags, new
    > > > methods and so I don't think it's the best solution. The only good
    > > > reason for putting new kind of entries in the lru would be to age them
    > > > too the same way as the other pages, but we don't need that with the bh
    > > > (they're just in, and we mostly care only about the page age, not the bh
    > > > age).
    > >
    > > For 2.5 I kind of like this idea. There is one issue though: to make
    > > this work really well we'd probably need a ->prepareforfreepage()
    > > or similar page op (which for page cache pages can be equal to writepage()
    > > ) which the vm can use to prepare this page for freeing.
    > If we stop using buffer_heads for pagecache I/O, we don't have this problem.
    > I'm showing a 20% reduction in CPU load for large reads. Which is a *lot*,
    > given that read load is dominated by copy_to_user.
    > 2.5 is significantly less efficient than 2.4 at this time. Some of that
    > seems to be due to worsened I-cache footprint, and a lot of it is due
    > to the way buffer_heads now have a BIO wrapper layer.

    Indeed, at the moment bio is making the thing more expensive in CPU
    terms, even if OTOH it makes rawio fly.

    > Take a look at submit_bh(). The writing is on the wall, guys.
    > -

    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2005-03-22 13:24    [W:0.023 / U:1.080 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site