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[156.34.49.251]) by smtp.gmail.com with ESMTPSA id u18sm9956618qka.25.2019.03.25.09.47.14 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 25 Mar 2019 09:47:14 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1h8Skj-0005QU-Qs; Mon, 25 Mar 2019 13:47:13 -0300 Date: Mon, 25 Mar 2019 13:47:13 -0300 From: Jason Gunthorpe To: Ira Weiny Cc: Dan Williams , Andrew Morton , John Hubbard , Michal Hocko , "Kirill A. Shutemov" , Peter Zijlstra , Benjamin Herrenschmidt , Paul Mackerras , "David S. Miller" , Martin Schwidefsky , Heiko Carstens , Rich Felker , Yoshinori Sato , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Ralf Baechle , James Hogan , linux-mm , Linux Kernel Mailing List , linux-mips@vger.kernel.org, linuxppc-dev , linux-s390 , Linux-sh , sparclinux@vger.kernel.org, linux-rdma@vger.kernel.org, "netdev@vger.kernel.org" Subject: Re: [RESEND 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast Message-ID: <20190325164713.GC9949@ziepe.ca> References: <20190317183438.2057-1-ira.weiny@intel.com> <20190317183438.2057-5-ira.weiny@intel.com> <20190325084225.GC16366@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190325084225.GC16366@iweiny-DESK2.sc.intel.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 25, 2019 at 01:42:26AM -0700, Ira Weiny wrote: > On Fri, Mar 22, 2019 at 03:12:55PM -0700, Dan Williams wrote: > > On Sun, Mar 17, 2019 at 7:36 PM wrote: > > > > > > From: Ira Weiny > > > > > > DAX pages were previously unprotected from longterm pins when users > > > called get_user_pages_fast(). > > > > > > Use the new FOLL_LONGTERM flag to check for DEVMAP pages and fall > > > back to regular GUP processing if a DEVMAP page is encountered. > > > > > > Signed-off-by: Ira Weiny > > > mm/gup.c | 29 +++++++++++++++++++++++++---- > > > 1 file changed, 25 insertions(+), 4 deletions(-) > > > > > > diff --git a/mm/gup.c b/mm/gup.c > > > index 0684a9536207..173db0c44678 100644 > > > +++ b/mm/gup.c > > > @@ -1600,6 +1600,9 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, > > > goto pte_unmap; > > > > > > if (pte_devmap(pte)) { > > > + if (unlikely(flags & FOLL_LONGTERM)) > > > + goto pte_unmap; > > > + > > > pgmap = get_dev_pagemap(pte_pfn(pte), pgmap); > > > if (unlikely(!pgmap)) { > > > undo_dev_pagemap(nr, nr_start, pages); > > > @@ -1739,8 +1742,11 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, > > > if (!pmd_access_permitted(orig, flags & FOLL_WRITE)) > > > return 0; > > > > > > - if (pmd_devmap(orig)) > > > + if (pmd_devmap(orig)) { > > > + if (unlikely(flags & FOLL_LONGTERM)) > > > + return 0; > > > return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr); > > > + } > > > > > > refs = 0; > > > page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); > > > @@ -1777,8 +1783,11 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, > > > if (!pud_access_permitted(orig, flags & FOLL_WRITE)) > > > return 0; > > > > > > - if (pud_devmap(orig)) > > > + if (pud_devmap(orig)) { > > > + if (unlikely(flags & FOLL_LONGTERM)) > > > + return 0; > > > return __gup_device_huge_pud(orig, pudp, addr, end, pages, nr); > > > + } > > > > > > refs = 0; > > > page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); > > > @@ -2066,8 +2075,20 @@ int get_user_pages_fast(unsigned long start, int nr_pages, > > > start += nr << PAGE_SHIFT; > > > pages += nr; > > > > > > - ret = get_user_pages_unlocked(start, nr_pages - nr, pages, > > > - gup_flags); > > > + if (gup_flags & FOLL_LONGTERM) { > > > + down_read(¤t->mm->mmap_sem); > > > + ret = __gup_longterm_locked(current, current->mm, > > > + start, nr_pages - nr, > > > + pages, NULL, gup_flags); > > > + up_read(¤t->mm->mmap_sem); > > > + } else { > > > + /* > > > + * retain FAULT_FOLL_ALLOW_RETRY optimization if > > > + * possible > > > + */ > > > + ret = get_user_pages_unlocked(start, nr_pages - nr, > > > + pages, gup_flags); > > > > I couldn't immediately grok why this path needs to branch on > > FOLL_LONGTERM? Won't get_user_pages_unlocked(..., FOLL_LONGTERM) do > > the right thing? > > Unfortunately holding the lock is required to support FOLL_LONGTERM (to check > the VMAs) but we don't want to hold the lock to be optimal (specifically allow > FAULT_FOLL_ALLOW_RETRY). So I'm maintaining the optimization for *_fast users > who do not specify FOLL_LONGTERM. > > Another way to do this would have been to define __gup_longterm_unlocked with > the above logic, but that seemed overkill at this point. get_user_pages_unlocked() is an exported symbol, shouldn't it work with the FOLL_LONGTERM flag? I think it should even though we have no user.. Otherwise the GUP API just gets more confusing. Jason