[lkml]   [2005]   [Jan]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH][5/?] count writeback pages in nr_scanned
On Wed, Jan 05, 2005 at 09:05:39PM -0800, Andrew Morton wrote:
> Andrea Arcangeli <> wrote:
> >
> > The fix is very simple and it is to call wait_on_page_writeback on one
> > of the pages under writeback.
> eek, no. That was causing waits of five seconds or more. Fixing this
> caused the single greatest improvement in page allocator latency in early
> 2.5. We're totally at the mercy of the elevator algorithm this way.
> If we're to improve things in there we want to wait on _any_ eligible page
> becoming reclaimable, not on a particular page.

I told you one way to fix it. I didn't guarantee it was the most
efficient one.

I sure agree waiting on any page to complete writeback is going to fix
it too. Exactly because this page was a "random" page anyway.

Still my point is that this is a bug, and I prefer to be slow and safe
like 2.4, than fast and unreliable like 2.6.

The slight improvement you suggested of waiting on _any_ random
PG_writeback to go away (instead of one particular one as I did in 2.4)
is going to fix the write throttling equally too as well as the 2.4
logic, but without introducing slowdown that 2.4 had.

It's easy to demonstrate: exactly because the page we pick is random
anyway, we can pick the first random one that has seen PG_writeback
transitioning from 1 to 0. The guarantee we get is the same in terms of
safety of the write throttling, but we also guarantee the best possible
latency this way. And the HZ/x hacks to avoid deadlocks will magically
go away too.
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 14:09    [W:0.080 / U:5.964 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site