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From:   "Huang\, Ying" <ying.huang@intel.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Daniel Jordan <daniel.m.jordan@oracle.com>
Subject: Re: [PATCH -mm -v4 00/21] mm, THP, swap: Swapout/swapin THP in one piece
References: <20180622035151.6676-1-ying.huang@intel.com>
        <20180627215144.73e98b01099191da59bff28c@linux-foundation.org>
        <20180704021153.GA3346@jagdpanzerIV>
        <878t6rvj12.fsf@yhuang-dev.intel.com>
        <20180704022734.GB3346@jagdpanzerIV>
Date:   Wed, 04 Jul 2018 10:59:55 +0800
In-Reply-To: <20180704022734.GB3346@jagdpanzerIV> (Sergey Senozhatsky's
        message of "Wed, 4 Jul 2018 11:27:34 +0900")
Message-ID: <87zhz7u2ms.fsf@yhuang-dev.intel.com>
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Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> writes:

> 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@intel.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.

Thanks!

> 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.

Yes.  I think so too.

Best Regards,
Huang, Ying