On Wed, Dec 12, 2001 at 07:45:45AM -0200, Rik van Riel wrote:
> On Wed, 12 Dec 2001, Andrea Arcangeli wrote:
> > On Wed, Dec 12, 2001 at 12:44:17AM -0800, Andrew Morton wrote:
> > > Oh.  Maybe the core design (whatever it is :)) is not finished,
> > > because it retains the bone-headed, dumb-to-the-point-of-astonishing
> > > misfeature which Linux VM has always had:
> > >
> > > If someone is linearly writing (or reading) a gigabyte file on a 64
> > > megabyte box they *don't* want the VM to evict every last little scrap
> > > of cache on behalf of data which they *obviously* do not want
> > > cached.
> >
> > The current design tries to detect this, at least much much better than
> > 2.2. This is why I disagree with Rik's patch of yesterday.  detecting
> > cache pollution is good also on the lowmem boxes (not only for DB).
> 
> Oh, absolutely. The problem just is that the current design
> has even worse problems where it doesn't put any pressure on
> pages which were touched twice an hour ago.

it does. See the refill_inactive pass.

> This leads to the situation that applications get OOM-killed
> to preserve buffer cache memory which hasn't been touched
> since bootup time.

It doesn't happen here.

At the very least the fix is the two liner from Andrew that forces a
nr_pages refile from active list, that will guarantee that whatever
happens we always roll the active list too, but the oom killing you are
experiencing is a problem of mainline, it definitely doesn't happen here
and the refill_inactive(0) cannot be the culprit because the active list
grows always to a relevant size and if during oom a few pages stays
untouched into the active list that's fine, those two pages couldn't
save us anyways so they'd better stay there so we don't trash.

> 
> There are ways to both have good behaviour on bulk IO and
> flush out old data which was in active use but no longer is.
> I believe these are called page aging and drop-behind.
> I've been thinking about achieving the wanted behaviour
> without these two, but haven't been able to come up with
> any algorithm which doesn't have some very bad side effects.
> 
> If you know a way of doing bulk IO properly and flushing out
> an old working set correctly, please let us know.
> 
> regards,
> 
> Rik
> -- 
> Shortwave goes a long way:  irc.starchat.net  #swl
> 
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Andrea
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