Messages in this thread | | | Date | Thu, 23 Oct 2008 09:16:00 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] Add block device speciffic splice write method |
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On Thu, Oct 23 2008, Andrew Morton wrote: > On Thu, 23 Oct 2008 08:51:13 +0200 Jens Axboe <jens.axboe@oracle.com> wrote: > > > On Wed, Oct 22 2008, Andrew Morton wrote: > > > On Thu, 23 Oct 2008 08:29:23 +0200 Jens Axboe <jens.axboe@oracle.com> wrote: > > > > > > > > But really it'd be better if the throttling happened down in > > > > > pipe_to_file(), on a per-page basis. As it stands we can dirty an > > > > > arbitrary number of pagecache pages without throttling. I think? > > > > > > > > That's pretty exactly why it isn't done in the actor, to avoid doing it > > > > per-page. As it's going to be PIPE_BUFFERS (16) pages max, I think this > > > > is better. > > > > > > > > Back in the splice early days, the balance_dirty_pages() actually showed > > > > up in profiles when it was done on a per-page basis. So I'm reluctant to > > > > change it :-) > > > > > > That's why (the misnamed) balance_dirty_pages_ratelimited() exists? > > > > I think that is what was used, but the details are a little hazy at this > > point. So I can't say for sure. > > All that function does is to bump a per-cpu variable and > once-per-thousand or so it does the balance. If it was causing > problems in the splice application we want to know, because write() > uses it!
Once per 8 or 32. If we haven't exceeded the dirty limit, calling it in the actor or at the end should not make a difference for splice, since we should be going into balance_dirty_pages() at most once.
Perhaps it was different some years ago, or perhaps the micro benchmarks were screwed. Or perhaps my memory is shot, can't say for sure :)
> > In this case it's moot anyway, since we can kill it. > > Nope, we can only remove it if the fd is O_SYNC||is_sync().
Right, I forgot this is still the buffered path.
-- Jens Axboe
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