Re: + mm-compaction-use-async-migration-for-__gfp_no_kswapd-and-enforce-no-writeback.patch added to -mm tree

[Andrea Arcangeli <aarcange@redhat.com>]

On Wed, Mar 23, 2011 at 03:01:33PM +0900, Minchan Kim wrote:
> Okay. I will look at result.
> If the problem happens again with reverted patch of page_alloc.c,
> Don't we have to investigate further the problem happens with SLUB or
> some driver's big memory allocation which is lower than 2M? We didn't
> see the problem allocation under 2M but async migration's history was
> short so we can't make sure it.

Yes, probably. This is also why I hope the page_alloc.c part didn't
make a difference. We kept it to be sure to make any sign of sync
migration to go away from the stack traces, but I hope it's not so
important anymore now. Reclaim eventually also becomes synchronous.

> Don't you want to add async migration for low order allocation like SLUB?
> If you don't want to do async migration low order allocation, we can
> add the check if (gfp_flags & __GFP_RETRY) && (order >= 9 or some
> threshold) for async migration?
> 
> My point is to avoid implicit hidden meaning of __GFP_NO_KSWAPD
> although __GFP_REPEAT already does it.

I see your point, so let's think about it after testing of the
reversal of the page_alloc.c change. If that's not necessary we just
reverse it and it already solves these concerns.

> If async migration is going on and meet the dirty page, the patch can
> return the -EBUSY so the page could put back to head of LRU but the
> old migration can be going on although the page is dirty.

Ok, but in term of LRU it's not like we're going to help much in
skipping the page in compaction, it'd leave the sync pages there, and
only list_del the async pages. I think it's mostly a cpu saving
optimization, I doubt the lru ordering will be much more accurate by
not doing list_del on the sync pages considering we would list_del
the rest but not the sync part.

> Totally agree with you.
> It's another topic and goes next time.
> 
> Thanks, Andrea.

Thanks to you for pointing out these problems.

Andrea

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>