lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Tue, 19 Oct 2021 12:21:09 -0700 From: Dan Williams <dan.j.williams@...el.com> To: Jason Gunthorpe <jgg@...pe.ca> Cc: Joao Martins <joao.m.martins@...cle.com>, Matthew Wilcox <willy@...radead.org>, Alex Sierra <alex.sierra@....com>, Andrew Morton <akpm@...ux-foundation.org>, "Kuehling, Felix" <Felix.Kuehling@....com>, Linux MM <linux-mm@...ck.org>, Ralph Campbell <rcampbell@...dia.com>, linux-ext4 <linux-ext4@...r.kernel.org>, linux-xfs <linux-xfs@...r.kernel.org>, amd-gfx list <amd-gfx@...ts.freedesktop.org>, Maling list - DRI developers <dri-devel@...ts.freedesktop.org>, Christoph Hellwig <hch@....de>, Jérôme Glisse <jglisse@...hat.com>, Alistair Popple <apopple@...dia.com>, Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>, Linux NVDIMM <nvdimm@...ts.linux.dev>, David Hildenbrand <david@...hat.com> Subject: Re: [PATCH v1 2/2] mm: remove extra ZONE_DEVICE struct page refcount On Tue, Oct 19, 2021 at 9:02 AM Jason Gunthorpe <jgg@...pe.ca> 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 > > discussion. > > > > 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. > > > 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. > > 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): > > > > https://lore.kernel.org/linux-mm/6a18179e-65f7-367d-89a9-d5162f10fef0@oracle.com/ > > 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 > behaviors. > > 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.
Powered by blists - more mailing lists