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SubjectRe: [PATCH] Re: PATCH: killing read_ahead[]
On Wed, 25 Oct 2000, Jeff V. Merkey wrote:
> Rik van Riel wrote:
> > On Wed, 25 Oct 2000, Jeff V. Merkey wrote:
> >
> > > I've reviewed the patch. It's affect seems minimal and will not
> > > break NWFS as proposed -- it looks like, however, it will reduce
> > > the performance slightly of EXT2/3 with iozone for read ahead
> > > since the first section of the patch limits the read ahead
> > > window size.
> >
> > Ummm, please read it again ;)
> >
> > The patch actually /increases/ the readahead size when
> > we start to read a file from the beginning.
> But only if the file is smaller than MIN_READAHEAD * 2, which
> would be the case for small files (which would read the whole
> file anyway, which is how the page cache behaves today anyway).

If the file is bigger than MIN_READAHEAD * 2, we will want
to read in the file in multiple IOs anyway.

If it turns out that we read that file sequentially, then
the kernel will read in a LARGER CHUNK next time, if it
turns out that we aren't using the file sequentially, we

The point of chosing the MIN_READAHEAD * 2 cutoff is that
I want to avoid the N+1 problem, where we do an IO for the
first MIN_READAHEAD pages and have to do a separate IO for
the last 1 page...


"What you're running that piece of shit Gnome?!?!"
-- Miguel de Icaza, UKUUG 2000

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