linux-kernel - Re: [PATCH v5 4/4] mm: Introduce per-thpsize swapin control policy

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Message-ID: <ZqcR_oZmVpi2TrHO@casper.infradead.org>
Date: Mon, 29 Jul 2024 04:52:30 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org, ying.huang@...el.com,
	baolin.wang@...ux.alibaba.com, chrisl@...nel.org, david@...hat.com,
	hannes@...xchg.org, hughd@...gle.com, kaleshsingh@...gle.com,
	kasong@...cent.com, linux-kernel@...r.kernel.org, mhocko@...e.com,
	minchan@...nel.org, nphamcs@...il.com, ryan.roberts@....com,
	senozhatsky@...omium.org, shakeel.butt@...ux.dev,
	shy828301@...il.com, surenb@...gle.com, v-songbaohua@...o.com,
	xiang@...nel.org, yosryahmed@...gle.com
Subject: Re: [PATCH v5 4/4] mm: Introduce per-thpsize swapin control policy

On Fri, Jul 26, 2024 at 09:46:18PM +1200, Barry Song wrote:
> A user space interface can be implemented to select different swap-in
> order policies, similar to the mTHP allocation order policy. We need
> a distinct policy because the performance characteristics of memory
> allocation differ significantly from those of swap-in. For example,
> SSD read speeds can be much slower than memory allocation. With
> policy selection, I believe we can implement mTHP swap-in for
> non-SWAP_SYNCHRONOUS scenarios as well. However, users need to understand
> the implications of their choices. I think that it's better to start
> with at least always never. I believe that we will add auto in the
> future to tune automatically, which can be used as default finally.

I strongly disagree.  Use the same sysctl as the other anonymous memory
allocations.