On Tue, Aug 12, 2014 at 11:45:32AM +0200, Vlastimil Babka wrote:

On 08/12/2014 07:17 AM, Minchan Kim wrote:

quoted

On Wed, Aug 06, 2014 at 04:18:33PM +0900, Joonsoo Kim wrote:

quoted

One solution to this problem is checking pageblock migratetype with
holding zone lock in __free_one_page() and I posted it before, but,
it didn't get welcome since it needs the hook in zone lock critical
section on freepath.

I didn't review your v1 but IMHO, this patchset is rather complex.

It is, but the complexity is in the isolation code, and not fast
paths, so that's justifiable IMHO.

quoted

Normally, we don't like adding more overhead in fast path but we did
several time on hotplug/cma, esp so I don't know a few more thing is
really hesitant.

This actually undoes most of the overhead, so I'm all for it. Better
than keep doing stuff the same way just because it was done
previously.

quoted

In addition, you proved by this patchset how this
isolation code looks ugly and fragile for race problem so I vote
adding more overhead in fast path if it can make code really simple.

Well, I recommend you to check out the v1 then :) That wasn't really
simple, that was even more hooks rechecking migratetypes at various
places of the fast paths, when merging buddies etc. This is much
better. The complexity is mostly in the isolation code, and the
overhead happens only during isolation.

Hmm... Okay.

I agree that this way is so complicated. In fact, the real save is just
one is_migrate_isolate_page() check in free_pcppages_bulk() and
this approach makes isolation process really complicated.

I guess that I could improve v1 patchset. How about waiting my
improved v1 and comparing v1' with v2?

If v1 is implemented cleanly, it may be better than this.
I want to try and compare. :)

Thanks.

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