linux-kernel - Re: [RFC v5 0/3] mm: make swapin readahead to gain more thp performance

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Date:	Fri, 26 Feb 2016 09:51:56 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Hugh Dickins <hughd@...gle.com>,
	Ebru Akagunduz <ebru.akagunduz@...il.com>
Cc:	linux-mm@...ck.org, akpm@...ux-foundation.org,
	kirill.shutemov@...ux.intel.com, n-horiguchi@...jp.nec.com,
	aarcange@...hat.com, iamjoonsoo.kim@....com, xiexiuqi@...wei.com,
	gorcunov@...nvz.org, linux-kernel@...r.kernel.org, mgorman@...e.de,
	rientjes@...gle.com, vbabka@...e.cz,
	aneesh.kumar@...ux.vnet.ibm.com, hannes@...xchg.org,
	mhocko@...e.cz, boaz@...xistor.com, raindel@...lanox.com
Subject: Re: [RFC v5 0/3] mm: make swapin readahead to gain more thp
 performance

On Thu, 2016-02-25 at 22:17 -0800, Hugh Dickins wrote:
> On Fri, 26 Feb 2016, Ebru Akagunduz wrote:
> > in Thu, Feb 25, 2016 at 05:35:50PM -0500, Rik van Riel wrote:
> 
> > > Am I forgetting anything obvious?
> > > 
> > > Is this too aggressive?
> > > 
> > > Not aggressive enough?
> > > 
> > > Could PGPGOUT + PGSWPOUT be a useful
> > > in-between between just PGSWPOUT or
> > > PGSTEAL_*?
> 
> I've no idea offhand, would have to study what each of those
> actually means: I'm really not familiar with them myself.

There are a few levels of page reclaim activity:

PGSTEAL_* - any page was reclaimed, this could just
            be file pages for streaming file IO,etc

PGPGOUT   - the VM wrote pages back to disk to reclaim
            them, this could include file pages

PGSWPOUT  - the VM wrote something to swap to reclaim
            memory

I am not sure which level of aggressiveness khugepaged
should check against, but my gut instinct would probably
be the second or third.

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