linux-kernel - Re: [PATCH RFC 0/4] mm: Remember young bit for migration entries

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Message-ID: <YuhS5DcwwNvy2Rkn@xz-m1.local>
Date:   Mon, 1 Aug 2022 18:25:40 -0400
From:   Peter Xu <peterx@...hat.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Nadav Amit <nadav.amit@...il.com>,
        Hugh Dickins <hughd@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andi Kleen <andi.kleen@...el.com>
Subject: Re: [PATCH RFC 0/4] mm: Remember young bit for migration entries

On Mon, Aug 01, 2022 at 01:33:28PM +0800, Huang, Ying wrote:
> If my understanding were correct, max_swapfile_size() provides a
> mechanism to identify the available bits with swp_entry_t and swap PTE
> considered.  We may take advantage of that?

That's an interesting trick, I'll have a closer look, thanks for the
pointer!

> 
> And according to commit 377eeaa8e11f ("x86/speculation/l1tf: Limit swap
> file size to MAX_PA/2"), the highest bit of swap offset needs to be 0 if
> L1TF mitigation is enabled.
> 
> Cced Andi for confirmation.

Yeah it'll be great to have a confirmation, hopefully max_swapfile_size()
should have covered that case.

-- 
Peter Xu