linux-kernel - Re: [PATCH -mm -v4 00/21] mm, THP, swap: Swapout/swapin THP in one piece

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Date:   Wed, 4 Jul 2018 11:27:34 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>
Subject: Re: [PATCH -mm -v4 00/21] mm, THP, swap: Swapout/swapin THP in one
 piece

On (07/04/18 10:20), Huang, Ying wrote:
> > On (06/27/18 21:51), Andrew Morton wrote:
> >> On Fri, 22 Jun 2018 11:51:30 +0800 "Huang, Ying" <ying.huang@...el.com> wrote:
> >> 
> >> > This is the final step of THP (Transparent Huge Page) swap
> >> > optimization.  After the first and second step, the splitting huge
> >> > page is delayed from almost the first step of swapout to after swapout
> >> > has been finished.  In this step, we avoid splitting THP for swapout
> >> > and swapout/swapin the THP in one piece.
> >> 
> >> It's a tremendously good performance improvement.  It's also a
> >> tremendously large patchset :(
> >
> > Will zswap gain a THP swap out/in support at some point?
> >
> >
> > mm/zswap.c: static int zswap_frontswap_store(...)
> > ...
> > 	/* THP isn't supported */
> > 	if (PageTransHuge(page)) {
> > 		ret = -EINVAL;
> > 		goto reject;
> > 	}
> 
> That's not on my TODO list.  Do you have interest to work on this?

I'd say I'm interested. Can't promise that I'll have enough spare time
any time soon, tho.

The numbers you posted do look fantastic indeed, embedded devices
[which normally use zswap/zram quite heavily] _probably_ should see
some performance improvement as well once zswap [and may be zram] can
handle THP.

	-ss