linux-kernel - Re: [RFC V3 PATCH] arm64: mm: swap: save and restore mte tags for large folios

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Date:   Fri, 17 Nov 2023 19:36:57 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Barry Song <21cnbao@...il.com>
Cc:     David Hildenbrand <david@...hat.com>, steven.price@....com,
        akpm@...ux-foundation.org, ryan.roberts@....com,
        catalin.marinas@....com, will@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...e.com,
        shy828301@...il.com, v-songbaohua@...o.com,
        wangkefeng.wang@...wei.com, xiang@...nel.org, ying.huang@...el.com,
        yuzhao@...gle.com
Subject: Re: [RFC V3 PATCH] arm64: mm: swap: save and restore mte tags for
 large folios

On Fri, Nov 17, 2023 at 07:47:00AM +0800, Barry Song wrote:
> This has been discussed. Steven, Ryan and I all don't think this is a good
> option. in case we have a large folio with 16 basepages, as do_swap_page
> can only map one base page for each page fault, that means we have
> to restore 16(tags we restore in each page fault) * 16(the times of page faults)
> for this large folio.

That doesn't seem all that hard to fix?  Call set_ptes() instead of
set_pte_at().  The biggest thing, I guess, is making sure that all
the PTEs you're going to set up are still pte_none().