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Date: Wed, 17 Aug 2022 09:09:01 -0300 From: Jason Gunthorpe <jgg@...dia.com> To: Alistair Popple <apopple@...dia.com> Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>, Chaitanya Kulkarni <kch@...dia.com>, Dan Williams <dan.j.williams@...el.com>, Felix Kuehling <Felix.Kuehling@....com>, John Hubbard <jhubbard@...dia.com>, Logan Gunthorpe <logang@...tatee.com>, Miaohe Lin <linmiaohe@...wei.com>, Muchun Song <songmuchun@...edance.com>, Ralph Campbell <rcampbell@...dia.com>, David Hildenbrand <david@...hat.com>, Matthew Wilcox <willy@...radead.org> Subject: Re: [PATCH v4 2/2] mm/gup.c: Refactor check_and_migrate_movable_pages() On Wed, Aug 17, 2022 at 12:01:58PM +1000, Alistair Popple wrote: > > Jason Gunthorpe <jgg@...dia.com> writes: > > > On Tue, Aug 16, 2022 at 03:29:20PM +1000, Alistair Popple wrote: > > > >> >> +static long check_and_migrate_movable_pages(unsigned long nr_pages, > >> >> + struct page **pages) > >> >> +{ > >> >> + int ret; > >> >> + unsigned long collected; > >> >> + LIST_HEAD(movable_page_list); > >> >> + > >> >> + collected = collect_longterm_unpinnable_pages(&movable_page_list, nr_pages, pages); > >> >> + if (!collected) > >> >> + return 0; > >> >> + > >> >> + ret = migrate_longterm_unpinnable_pages(&movable_page_list, nr_pages, pages); > >> >> + if (!ret) > >> >> + return -EAGAIN; > >> >> + else > >> >> + return ret; > >> > > >> > I would drop the else path and just return zero > >> > >> Unless I've misunderstood you I don't think that's correct though. > >> check_and_migrate_movable_pages() needs to return one of 3 conditions: > >> > >> - 0: All pages are in the correct zone and are still pinned (ie. "success"). > >> - -EAGAIN: Some pages were migrated, all pages need re-pinning. > >> - errno: Migration failed, pins were dropped and PUP should fail. > >> > >> John's suggested comment update spells this out more clearly. > > > > But that is not what it does.. > > > > if (!ret) == if (ret != 0) > > Huh? Unless I'm misinterpretting you or am really behind on coffee > if (!ret) is equivalent to if (ret == 0), not if (ret != 0). Oh Dear, maybe I am still a bit jetlagged Regardless, it is confusingly written :) Sorry, Jason
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