On Thu 28-07-16 07:33:19, NeilBrown wrote:

On Thu, Jul 28 2016, Michal Hocko wrote:

quoted

On Wed 27-07-16 13:43:35, NeilBrown wrote:

quoted

On Mon, Jul 25 2016, Michal Hocko wrote:

quoted

On Sat 23-07-16 10:12:24, NeilBrown wrote:

[...]

quoted

So should there be a limit on dirty
pages in the swap cache just like there is for dirty pages in any
filesystem (the max_dirty_ratio thing) ??
Maybe there is?

There is no limit AFAIK. We are relying that the reclaim is throttled
when necessary.

Is that a bit indirect?

Yes it is. Dunno, how much of a problem is that, though.

It is hard to tell without a clear big-picture.
Something to keep in mind anyway.

quoted

quoted

I think we'd end up with cleaner code if we removed the cute-hacks.  And
we'd be able to use 6 more GFP flags!!  (though I do wonder if we really
need all those 26).

Well, maybe we are able to remove those hacks, I wouldn't definitely
be opposed.  But right now I am not even convinced that the mempool
specific gfp flags is the right way to go.

I'm not suggesting a mempool-specific gfp flag.  I'm suggesting a
transient-allocation gfp flag, which would be quite useful for mempool.

Can you give more details on why using a gfp flag isn't your first choice
for guiding what happens when the system is trying to get a free page
:-?

If we get rid of throttle_vm_writeout then I guess it might turn out to
be unnecessary. There are other places which will still throttle but I
believe those should be kept regardless of who is doing the allocation
because they are helping the LRU scanning sane. I might be wrong here
and bailing out from the reclaim rather than waiting would turn out
better for some users but I would like to see whether the first approach
works reasonably well.
-- 
Michal Hocko
SUSE Labs

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