linux-kernel - Re: [PATCH v11 09/12] mm: implement LUF(Lazy Unmap Flush) defering tlb flush when folios get unmapped

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Date: Mon, 3 Jun 2024 20:00:52 +0200
From: David Hildenbrand <david@...hat.com>
To: Matthew Wilcox <willy@...radead.org>, Dave Hansen <dave.hansen@...el.com>
Cc: Byungchul Park <byungchul@...com>,
 Byungchul Park <lkml.byungchul.park@...il.com>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, kernel_team@...ynix.com,
 akpm@...ux-foundation.org, ying.huang@...el.com, vernhao@...cent.com,
 mgorman@...hsingularity.net, hughd@...gle.com, peterz@...radead.org,
 luto@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, rjgolo@...il.com
Subject: Re: [PATCH v11 09/12] mm: implement LUF(Lazy Unmap Flush) defering
 tlb flush when folios get unmapped

On 03.06.24 19:01, Matthew Wilcox wrote:
> On Mon, Jun 03, 2024 at 09:37:46AM -0700, Dave Hansen wrote:
>> Yeah, we'd need some equivalent of a PTE marker, but for the page cache.
>>   Presumably some xa_value() that means a reader has to go do a
>> luf_flush() before going any farther.
> 
> I can allocate one for that.  We've got something like 1000 currently
> unused values which can't be mistaken for anything else.

I'm curious when to set that, though.

While migrating/reclaiming, when unmapping the folio from the page 
tables, the folio is still valid in the page cache. So at the point in 
time of unmapping from one process, we cannot simply replace the folio 
in the page cache by some other value -- I think.

Maybe it's all easier than I think.

-- 
Cheers,

David / dhildenb