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Date: Fri, 18 Feb 2022 14:37:55 -0500 From: Felix Kuehling <felix.kuehling@....com> To: Jason Gunthorpe <jgg@...dia.com> Cc: David Hildenbrand <david@...hat.com>, Alistair Popple <apopple@...dia.com>, Christoph Hellwig <hch@....de>, Alex Sierra <alex.sierra@....com>, akpm@...ux-foundation.org, linux-mm@...ck.org, rcampbell@...dia.com, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, jglisse@...hat.com, willy@...radead.org Subject: Re: [PATCH v6 01/10] mm: add zone device coherent type memory support Am 2022-02-18 um 14:26 schrieb Jason Gunthorpe: > On Fri, Feb 18, 2022 at 02:20:45PM -0500, Felix Kuehling wrote: >> Am 2022-02-17 um 19:19 schrieb Jason Gunthorpe: >>> On Thu, Feb 17, 2022 at 04:12:20PM -0500, Felix Kuehling wrote: >>> >>>> I'm thinking of a more theoretical approach: Instead of auditing all users, >>>> I'd ask, what are the invariants that a vm_normal_page should have. Then >>>> check, whether our DEVICE_COHERENT pages satisfy them. But maybe the concept >>>> of a vm_normal_page isn't defined clearly enough for that. >>> I would say the expectation is that only 'page cache and anon' pages >>> are returned - ie the first union in struct page >>> >>> This is because the first file in your list I looked at: >>> >>> static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, >>> unsigned long addr, unsigned long end, >>> struct mm_walk *walk) >>> >>> { >>> page = vm_normal_page(vma, addr, ptent); >>> [..] >>> if (pageout) { >>> if (!isolate_lru_page(page)) { >>> >>> Uses the LRU field, so this is incompatible with all the other page >>> types. >>> >>> One mitigation of this might be to formally make vm_normal_page() == >>> 'pte to page cache and anon page' and add a new function that is 'pte >>> to any struct page' >>> >>> Then go through and sort callers as appropriate. >>> >>> The 'pte to page cache and anon page' can detect ZONE_DEVICE by >>> calling is_zone_device_page() insted of pte_devmap() and then continue >>> to return NULL. This same trick will fix GUP_fast. >> Sounds good to me. What about vm_normal_page_pmd? Should we remove the >> pmd_devmap check from that function as well. I'm not even sure what a huge >> zone_device page would look like, but maybe that's a worthwhile future >> optimization for our driver. > IIRC there are other problems here as PMDs are currently wired to THPs > and not general at all.. > > We have huge zone_device pages, it is just any compound page of > contiguous pfns - you should be aggregating any contiguous string of > logical PFNs together into a folio for performance. If the folio is > stuffed into a PMD or not is a different question.. > >> I'd propose the function names vm_normal_page and vm_normal_or_device_page >> for the two functions you described. > I wouldn't say device_page, it should be any type of page - though > device_page is the only other option ATM, AFIAK. Ok, then how about vm_normal_lru_page and vm_normal_any_page? Regards, Felix > >> current vm_normal_page with the pte_devmap check removed. vm_normal_page >> could be implemented as a wrapper around vm_normal_or_device_page, which >> just adds the !is_zone_device_page() check. > Yes > > Jason
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