From: Jason Gunthorpe <jgg@ziepe.ca>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Peter Xu" <peterx@redhat.com>, "Jan Kara" <jack@suse.cz>,
"Claudio Imbrenda" <imbrenda@linux.ibm.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
"Alex Williamson" <alex.williamson@redhat.com>,
"Andrea Arcangeli" <aarcange@redhat.com>,
"Jérôme Glisse" <jglisse@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org
Subject: Re: [PATCH 4/4] mm/gup: remove get_user_pages_locked()
Date: Mon, 31 Jan 2022 09:36:12 -0400 [thread overview]
Message-ID: <20220131133612.GW8034@ziepe.ca> (raw)
In-Reply-To: <20220131051752.447699-5-jhubbard@nvidia.com>
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
next prev parent reply other threads:[~2022-01-31 13:36 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-31 5:17 [PATCH 0/4] mm/gup: some cleanups John Hubbard
2022-01-31 5:17 ` [PATCH 1/4] mm: Fix invalid page pointer returned with FOLL_PIN gups John Hubbard
2022-02-02 14:04 ` Christoph Hellwig
2022-01-31 5:17 ` [PATCH 2/4] mm/gup: clean up follow_pfn_pte() slightly John Hubbard
2022-01-31 13:36 ` Jason Gunthorpe
2022-01-31 5:17 ` [PATCH 3/4] mm/gup: remove unused pin_user_pages_locked() John Hubbard
2022-01-31 14:06 ` David Hildenbrand
2022-01-31 14:43 ` Jason Gunthorpe
2022-02-02 14:05 ` Christoph Hellwig
2022-01-31 5:17 ` [PATCH 4/4] mm/gup: remove get_user_pages_locked() John Hubbard
2022-01-31 12:05 ` Jan Kara
2022-01-31 20:01 ` John Hubbard
2022-01-31 13:36 ` Jason Gunthorpe [this message]
2022-01-31 20:01 ` John Hubbard
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