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[142.162.113.129]) by smtp.gmail.com with ESMTPSA id 22sm8132398qtw.75.2022.01.31.05.36.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 31 Jan 2022 05:36:13 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1nEWqq-009WAO-6O; Mon, 31 Jan 2022 09:36:12 -0400 Date: Mon, 31 Jan 2022 09:36:12 -0400 From: Jason Gunthorpe To: John Hubbard Cc: Andrew Morton , Peter Xu , Jan Kara , Claudio Imbrenda , "Kirill A . Shutemov" , Alex Williamson , Andrea Arcangeli , =?utf-8?B?SsOpcsO0bWU=?= Glisse , LKML , linux-mm@kvack.org Subject: Re: [PATCH 4/4] mm/gup: remove get_user_pages_locked() Message-ID: <20220131133612.GW8034@ziepe.ca> References: <20220131051752.447699-1-jhubbard@nvidia.com> <20220131051752.447699-5-jhubbard@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220131051752.447699-5-jhubbard@nvidia.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jan 30, 2022 at 09:17:52PM -0800, John Hubbard wrote: > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 028e8dd82b44..040d88354cfa 100644 > +++ b/mm/mempolicy.c > @@ -907,17 +907,15 @@ static void get_policy_nodemask(struct mempolicy *p, nodemask_t *nodes) > static int lookup_node(struct mm_struct *mm, unsigned long addr) > { > struct page *p = NULL; > - int err; > + int ret; > > - int locked = 1; > - err = get_user_pages_locked(addr & PAGE_MASK, 1, 0, &p, &locked); > - if (err > 0) { > - err = page_to_nid(p); > + mmap_assert_locked(mm); > + ret = get_user_pages(addr & PAGE_MASK, 1, 0, &p, NULL); > + if (ret > 0) { > + ret = page_to_nid(p); > put_page(p); > } > - if (locked) > - mmap_read_unlock(mm); > - return err; > + return ret; > } > > /* Retrieve NUMA policy */ > @@ -968,15 +966,15 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask, > if (flags & MPOL_F_NODE) { > if (flags & MPOL_F_ADDR) { > /* > - * Take a refcount on the mpol, lookup_node() > - * will drop the mmap_lock, so after calling > - * lookup_node() only "pol" remains valid, "vma" > - * is stale. > + * Take a refcount on the mpol, because we are about to > + * drop the mmap_lock, after which only "pol" remains > + * valid, "vma" is stale. > */ > pol_refcount = pol; > vma = NULL; > mpol_get(pol); > err = lookup_node(mm, addr); > + mmap_read_unlock(mm); How about move the mmap_read_unlock up one line and then use get_user_pages_fast() I'm guessing in most cases here the PTE will be present so that should be a net win? Jason