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Date: Fri, 18 Feb 2022 14:20:45 -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 2022-02-17 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. I'd propose the function names vm_normal_page and vm_normal_or_device_page for the two functions you described. The latter would basically be the 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. Regards, Felix > > Jason >
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