From: Joao Martins <email@example.com>
To: Dan Williams <firstname.lastname@example.org>, Jason Gunthorpe <email@example.com>
Cc: "Matthew Wilcox" <firstname.lastname@example.org>,
"Alex Sierra" <email@example.com>,
"Andrew Morton" <firstname.lastname@example.org>,
"Kuehling, Felix" <Felix.Kuehling@amd.com>,
"Linux MM" <email@example.com>,
"Ralph Campbell" <firstname.lastname@example.org>,
"amd-gfx list" <email@example.com>,
"Maling list - DRI developers" <firstname.lastname@example.org>,
"Christoph Hellwig" <email@example.com>,
"Jérôme Glisse" <firstname.lastname@example.org>,
"Alistair Popple" <email@example.com>,
"Vishal Verma" <firstname.lastname@example.org>,
"Dave Jiang" <email@example.com>,
"Linux NVDIMM" <firstname.lastname@example.org>,
"David Hildenbrand" <email@example.com>
Subject: Re: [PATCH v1 2/2] mm: remove extra ZONE_DEVICE struct page refcount
Date: Wed, 20 Oct 2021 18:06:51 +0100 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
On 10/19/21 20:21, Dan Williams wrote:
> On Tue, Oct 19, 2021 at 9:02 AM Jason Gunthorpe <email@example.com> wrote:
>> On Tue, Oct 19, 2021 at 04:13:34PM +0100, Joao Martins wrote:
>>> On 10/19/21 00:06, Jason Gunthorpe wrote:
>>>> On Mon, Oct 18, 2021 at 12:37:30PM -0700, Dan Williams wrote:
>>>>>> device-dax uses PUD, along with TTM, they are the only places. I'm not
>>>>>> sure TTM is a real place though.
>>>>> I was setting device-dax aside because it can use Joao's changes to
>>>>> get compound-page support.
>>>> Ideally, but that ideas in that patch series have been floating around
>>>> for a long time now..
>>> The current status of the series misses a Rb on patches 6,7,10,12-14.
>>> Well, patch 8 too should now drop its tag, considering the latest
>>> If it helps moving things forward I could split my series further into:
>>> 1) the compound page introduction (patches 1-7) of my aforementioned series
>>> 2) vmemmap deduplication for memory gains (patches 9-14)
>>> 3) gup improvements (patch 8 and gup-slow improvements)
>> I would split it, yes..
>> I think we can see a general consensus that making compound_head/etc
>> work consistently with how THP uses it will provide value and
>> opportunity for optimization going forward.
I'll go do that. Meanwhile, I'll wait a couple days for Dan to review the
dax subsystem patches (6 & 7), or otherwise send them over.
>>> Whats the benefit between preventing longterm at start
>>> versus only after mounting the filesystem? Or is the intended future purpose
>>> to pass more context into an holder potential future callback e.g. nack longterm
>>> pins on a page basis?
>> I understood Dan's remark that the device-dax path allows
>> FOLL_LONGTERM and the FSDAX path does not ?
>> Which, IIRC, today is signaled basd on vma properties and in all cases
>> fast-gup is denied.
> Yeah, I forgot that 7af75561e171 eliminated any possibility of
> longterm-gup-fast for device-dax, let's not disturb that status quo.
I am slightly confused by this comment -- the status quo is what we are
questioning here -- And we talked about changing that in the past too
(thread below), that longterm-gup-fast was an oversight that that commit
was only applicable to fsdax. [Maybe this is just my english confusion]
>>> Maybe we can start by at least not add any flags and just prevent
>>> FOLL_LONGTERM on fsdax -- which I guess was the original purpose of
>>> commit 7af75561e171 ("mm/gup: add FOLL_LONGTERM capability to GUP fast").
>>> This patch (which I can formally send) has a sketch of that (below scissors mark):
>> Yes, basically, whatever test we want for 'deny fast gup foll
>> longterm' is fine.
>> Personally I'd like to see us move toward a set of flag specifying
>> each special behavior and not a collection of types that imply special
>> Eg we have at least:
>> - Block gup fast on foll_longterm
>> - Capture the refcount ==1 and use the pgmap free hook
>> (confusingly called page_is_devmap_managed())
>> - Always use a swap entry
>> - page->index/mapping are used in the usual file based way?
>> Probably more things..
> Yes, agree with the principle of reducing type-implied special casing.
Moving from implicit devmap types to pgmap::flags is rather simple fixup.
And I suppose (respectivally) PGMAP_NO_PINF_LONGTERM, PGMAP_MANAGED_FREE_PAGE,
PGMAP_USE_SWAP_ENTRY, etc, etc.
next prev parent reply other threads:[~2021-10-20 17:07 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-14 15:39 [PATCH v1 0/2] mm: remove extra ZONE_DEVICE struct page refcount Alex Sierra
2021-10-14 15:39 ` [PATCH v1 1/2] ext4/xfs: add page refcount helper Alex Sierra
2021-10-14 16:25 ` Jason Gunthorpe
2021-10-14 16:40 ` Matthew Wilcox
2021-10-14 15:39 ` [PATCH v1 2/2] mm: remove extra ZONE_DEVICE struct page refcount Alex Sierra
2021-10-14 16:52 ` Matthew Wilcox
2021-10-14 17:06 ` Jason Gunthorpe
2021-10-14 17:35 ` Ralph Campbell
2021-10-14 18:01 ` Jason Gunthorpe
2021-10-14 20:57 ` Ralph Campbell
2021-10-15 3:45 ` Sierra Guiza, Alejandro (Alex)
2021-10-15 11:06 ` Jason Gunthorpe
2021-10-14 18:43 ` Matthew Wilcox
2021-10-14 19:01 ` Dan Williams
2021-10-14 23:06 ` Jason Gunthorpe
2021-10-15 1:37 ` Dan Williams
2021-10-16 15:44 ` Jason Gunthorpe
2021-10-16 16:39 ` Matthew Wilcox
2021-10-17 18:20 ` Dan Williams
2021-10-17 18:35 ` Dan Williams
2021-10-18 18:25 ` Jason Gunthorpe
2021-10-18 19:37 ` Dan Williams
2021-10-18 23:06 ` Jason Gunthorpe
2021-10-19 15:13 ` Joao Martins
2021-10-19 16:01 ` Jason Gunthorpe
2021-10-19 19:21 ` Dan Williams
2021-10-20 17:06 ` Joao Martins [this message]
2021-10-20 17:12 ` Dan Williams
2021-10-20 18:51 ` Joao Martins
2021-11-15 19:33 [PATCH v1 0/2] Remove extra ZONE_DEVICE " Alex Sierra
2021-11-15 19:33 ` [PATCH v1 2/2] mm: remove extra ZONE_DEVICE struct " Alex Sierra
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