Re: [PATCH 1/1] arm64: mm: swap: support THP_SWAP on hardware with MTE

[David Hildenbrand <david@redhat.com>]

On 27.03.24 15:53, Matthew Wilcox wrote:
> On Sat, Mar 23, 2024 at 12:41:36AM +1300, Barry Song wrote:
>> Commit d0637c505f8a1 ("arm64: enable THP_SWAP for arm64") brings up
>> THP_SWAP on ARM64, but it doesn't enable THP_SWP on hardware with
>> MTE as the MTE code works with the assumption tags save/restore is
>> always handling a folio with only one page.
>>
>> The limitation should be removed as more and more ARM64 SoCs have
>> this feature. Co-existence of MTE and THP_SWAP becomes more and
>> more important.
>>
>> This patch makes MTE tags saving support large folios, then we don't
>> need to split large folios into base pages for swapping out on ARM64
>> SoCs with MTE any more.
> 
> Can we go further than this patch and only support PG_mte_tagged and
> PG_mte_lock on folio->flags instead of page->flags?  We're down to using

I think we discussed that already and what I learned is that it "gets a 
bit complicated". But I'm hoping we can get that discussion started again.

> page->flags for these two MTE bits, a whole lot of s390 junk, PG_hwpoison,
> PG_head, PG_anon_exclusive and Zone/Section/Node/KASAN/last_cpupid.

... just like PG_anon_exclusive "gets a bit complicated". Well, I think 
I might have finally found a way to make it work, I'll only have to 
uglify fork() a bit.

-- 
Cheers,

David / dhildenb