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

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Date:   Wed, 15 Nov 2023 14:45:42 -0800
From:   Yang Shi <shy828301@...il.com>
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,
        v-songbaohua@...o.com, wangkefeng.wang@...wei.com,
        willy@...radead.org, 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 Wed, Nov 15, 2023 at 12:49 PM Barry Song <21cnbao@...il.com> wrote:
>
> On Wed, Nov 15, 2023 at 11:16 PM David Hildenbrand <david@...hat.com> wrote:
> >
> > On 14.11.23 02:43, Barry Song wrote:
> > > This patch makes MTE tags saving and restoring support large folios,
> > > then we don't need to split them into base pages for swapping out
> > > on ARM64 SoCs with MTE.
> > >
> > > arch_prepare_to_swap() should take folio rather than page as parameter
> > > because we support THP swap-out as a whole.
> > >
> > > Meanwhile, arch_swap_restore() should use page parameter rather than
> > > folio as swap-in always works at the granularity of base pages right
> > > now.
> >
> > ... but then we always have order-0 folios and can pass a folio, or what
> > am I missing?
>
> Hi David,
> you missed the discussion here:
>
> https://lore.kernel.org/lkml/CAGsJ_4yXjex8txgEGt7+WMKp4uDQTn-fR06ijv4Ac68MkhjMDw@mail.gmail.com/
> https://lore.kernel.org/lkml/CAGsJ_4xmBAcApyK8NgVQeX_Znp5e8D4fbbhGguOkNzmh1Veocg@mail.gmail.com/
>
> >
> > >
> > > arch_thp_swp_supported() is dropped since ARM64 MTE was the only one
> > > who needed it.
> >
> > Can we do that separately?
>
> i think it is ok.

IMHO keeping it in this patch makes more sense. IIRC removing
arch_thp_swp_supported() is just because this patch made swapping
large folio with MTE more efficiently.

>
> >
> > --
> > Cheers,
> >
> > David / dhildenb
> >
>
> Thanks
> Barry