From: Steven Price <steven.price@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
Dave Hansen <dave.hansen@intel.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
linux-arch@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Arnd Bergmann <arnd@arndb.de>, Hugh Dickins <hughd@google.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH 2/4] mm: Add arch hooks for saving/restoring tags
Date: Thu, 23 Apr 2020 13:37:21 +0100 [thread overview]
Message-ID: <380bdf0b-aa7c-399c-d16d-b2aecd3f363c@arm.com> (raw)
In-Reply-To: <20200423090919.GA4963@gaia>
On 23/04/2020 10:09, Catalin Marinas wrote:
> On Wed, Apr 22, 2020 at 11:08:10AM -0700, Dave Hansen wrote:
>> On 4/22/20 7:25 AM, Steven Price wrote:
>>> Three new hooks are added to the swap code:
>>> * arch_prepare_to_swap() and
>>> * arch_swap_invalidate_page() / arch_swap_invalidate_area().
>>> One new hook is added to shmem:
>>> * arch_swap_restore_tags()
>>
>> How do the tags get restored outside of the shmem path? I was expecting
>> to see more arch_swap_restore_tags() sites.
>
> The restoring is done via set_pte_at() -> mte_sync_tags() ->
> mte_restore_tags() in the arch code (see patch 3).
> arch_swap_restore_tags() just calls mte_restore_tags() directly.
>
> shmem is slightly problematic as it moves the page from the swap cache
> to the shmem one and I think arch_swap_invalidate_page() would have
> already been called by the time we get to set_pte_at() (Steven can
> correct me if I got this wrong).
That's correct - shmem can pull in pages (into it's own cache) and
invalidate the swap entries without any process having a PTE restored.
So we need to hook shmem to restore the tags even though there's no PTE
restored yet.
The set_pte_at() 'trick' enables delaying the restoring of the tags (in
the usual case) until the I/O for the page has completed, which might be
necessary in some cases if the I/O can clobber the tags in memory. I
couldn't find a better way of hooking this.
Steve
next prev parent reply other threads:[~2020-04-23 12:37 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-22 14:25 [PATCH 0/4] arm64: MTE swap and hibernation support Steven Price
2020-04-22 14:25 ` [PATCH 1/4] mm: Add PG_ARCH_2 page flag Steven Price
2020-04-22 14:25 ` [PATCH 2/4] mm: Add arch hooks for saving/restoring tags Steven Price
2020-04-22 18:08 ` Dave Hansen
2020-04-23 9:09 ` Catalin Marinas
2020-04-23 12:37 ` Steven Price [this message]
2020-04-22 14:25 ` [PATCH 3/4] arm64: mte: Enable swap of tagged pages Steven Price
2020-04-22 18:34 ` Dave Hansen
2020-04-23 13:51 ` Steven Price
2020-05-03 15:29 ` Catalin Marinas
2020-05-04 12:53 ` Steven Price
2020-04-22 14:25 ` [PATCH 4/4] arm64: mte: Save tags when hibernating Steven Price
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