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Date: Mon, 26 Sep 2022 11:36:11 -0300 From: Jason Gunthorpe <jgg@...dia.com> To: Alistair Popple <apopple@...dia.com> Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, Felix Kuehling <Felix.Kuehling@....com>, Alex Deucher <alexander.deucher@....com>, Christian König <christian.koenig@....com>, "Pan, Xinhui" <Xinhui.Pan@....com>, David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>, Ben Skeggs <bskeggs@...hat.com>, Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>, Ralph Campbell <rcampbell@...dia.com>, "Matthew Wilcox (Oracle)" <willy@...radead.org>, Alex Sierra <alex.sierra@....com>, John Hubbard <jhubbard@...dia.com>, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org, nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, Dan Williams <dan.j.williams@...el.com> Subject: Re: [PATCH 2/7] mm: Free device private pages have zero refcount On Mon, Sep 26, 2022 at 04:03:06PM +1000, Alistair Popple wrote: > Since 27674ef6c73f ("mm: remove the extra ZONE_DEVICE struct page > refcount") device private pages have no longer had an extra reference > count when the page is in use. However before handing them back to the > owning device driver we add an extra reference count such that free > pages have a reference count of one. > > This makes it difficult to tell if a page is free or not because both > free and in use pages will have a non-zero refcount. Instead we should > return pages to the drivers page allocator with a zero reference count. > Kernel code can then safely use kernel functions such as > get_page_unless_zero(). > > Signed-off-by: Alistair Popple <apopple@...dia.com> > --- > arch/powerpc/kvm/book3s_hv_uvmem.c | 1 + > drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 1 + > drivers/gpu/drm/nouveau/nouveau_dmem.c | 1 + > lib/test_hmm.c | 1 + > mm/memremap.c | 5 ----- > mm/page_alloc.c | 6 ++++++ > 6 files changed, 10 insertions(+), 5 deletions(-) I think this is a great idea, but I'm surprised no dax stuff is touched here? Jason
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