Hi Kame,

On 06/23/2012 01:45 PM, Kamezawa Hiroyuki wrote:

(2012/06/22 15:57), Minchan Kim wrote:

quoted

Hi John,

On 06/22/2012 04:21 AM, John Stultz wrote:

quoted

On 06/18/2012 10:49 PM, Minchan Kim wrote:

quoted

Hi everybody!

Recently, there are some efforts to handle system memory pressure.

1) low memory notification - [1]
2) fallocate(VOLATILE) - [2]
3) fadvise(NOREUSE) - [3]

For them, I would like to add new LRU list, aka "Ereclaimable" which
is opposite of "unevictable".
Reclaimable LRU list includes _easy_ reclaimable pages.
For example, easy reclaimable pages are following as.

1. invalidated but remained LRU list.
2. pageout pages for reclaim(PG_reclaim pages)
3. fadvise(NOREUSE)
4. fallocate(VOLATILE)

Their pages shouldn't stir normal LRU list and compaction might not
migrate them, even.
Reclaimer can reclaim Ereclaimable pages before normal lru list and
will avoid unnecessary
swapout in anon pages in easy-reclaimable LRU list.

I was hoping there would be further comment on this by more core VM
devs, but so far things have been quiet (is everyone on vacation?).

At least, there are no dissent comment until now.
Let be a positive. :)

I think this is interesting approach. Major concern is how to guarantee
EReclaimable
pages are really EReclaimable...Do you have any idea ? madviced pages
are really
EReclaimable ?

I would like to select just discardable pages.

1. unmapped file page 
2. PG_reclaimed page - (that pages would have no mapped and a candidate 
   for reclaim ASAP)
3. fallocate(VOLATILE) - (We can just discard them without swapout)
4. madvise(MADV_DONTNEED)/fadvise(NOREUSE) -
   (It could be difficult than (1,2,3) but it's very likely to reclaim easily than others.

A (very) small concern is will you use one more page-flags for this ? ;)

Maybe and it could be a serious problem on 32 bit machine.
I didn't dive into that but I guess we can reuse PG_reclaim bit.
PG_reclaim is always used by with !PageActive and Ereclaimable LRU list doesn't have 
active LRU list. so we can change following as

- #define PG_reclaim
+ #define PG_Ereclaim

SetPageReclaim(page)
{
	page->flags |= (PG_Ereclaim|PG_active);
}

TestPageReclaim(page)
{
	if (((page->flags && PG_Ereclaim|PG_active)) == (PG_Ereclaim|PG_active)) 
		return true;
	return false;
}

SetPageEreclaim(page)
{
	page->flags |= PG_Ereclaim;
}

Thanks for the comment, Kame.
-- 
Kind regards,
Minchan Kim

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