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From: David Hildenbrand <david@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Viacheslav Dubeyko <slava@dubeyko.com>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	linux-mm@kvack.org, Hugh Dickins <hughd@google.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: Issue with 8K folio size in __filemap_get_folio()
Date: Mon, 4 Dec 2023 18:22:17 +0100	[thread overview]
Message-ID: <d830e87d-9937-43c8-b29b-826c31e31e9f@redhat.com> (raw)
In-Reply-To: <ZW4JqpKAc56aIUhF@casper.infradead.org>

On 04.12.23 18:17, Matthew Wilcox wrote:
> On Mon, Dec 04, 2023 at 04:09:36PM +0100, David Hildenbrand wrote:
>> I think for the pagecache it should work. In the context of [1], a total
>> mapcount would likely still be possible. Anything beyond that likely not, if
>> we ever care.
> 
> I confess I hadn't gone through your patches.
> 
> https://lore.kernel.org/all/20231124132626.235350-8-david@redhat.com/
> 
> is the critical one.  It's actually going to walk off the end of order-2
> folios today (which we'll create, eg with XFS).

Note that order-2 only uses _rmap_val0. So that *should* work  as 
expected (and that layout resulted in the best cache behavior, weirdly 
enough).

> 
> You can put _rmap_val0 and _rmap_val1 in page2 and _rmap_val2-5 in page3
> to fix this.  Once we're allocating order-1 folios, I think you can
> avoid this scheme and just check page0 and page1 mapcounts independently.

I could put _rmap_val0 in page1 after I get rid of  		_folio_nr_pages. 
That would make it work on 64bit.

But yeah, it feels kind of stupid to do elaborate tracking for "it's 2 
pages". OTOH, less special-casing can be preferable.

-- 
Cheers,

David / dhildenb



      reply	other threads:[~2023-12-04 17:22 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <B467D07C-00D2-47C6-A034-2D88FE88A092@dubeyko.com>
2023-12-03 21:27 ` Issue with 8K folio size in __filemap_get_folio() Matthew Wilcox
2023-12-03 23:12   ` Matthew Wilcox
2023-12-04  5:57     ` Hugh Dickins
2023-12-04 15:09     ` David Hildenbrand
2023-12-04 16:51       ` David Hildenbrand
2023-12-04 17:17       ` Matthew Wilcox
2023-12-04 17:22         ` David Hildenbrand [this message]

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