The patch titled
Subject: mm: change lookup_node() to use get_user_pages_fast()
has been removed from the -mm tree. Its filename was
mm-change-lookup_node-to-use-get_user_pages_fast.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: John Hubbard <jhubbard@xxxxxxxxxx>
Subject: mm: change lookup_node() to use get_user_pages_fast()
The purpose of calling get_user_pages_locked() from lookup_node() was to
allow for unlocking the mmap_lock when reading a page from the disk during
a page fault (hidden behind VM_FAULT_RETRY). The idea was to reduce
contention on the heavily-used mmap_lock. (Thanks to Jan Kara for clearly
pointing that out, and in fact I've used some of his wording here.)
However, it is unlikely for lookup_node() to take a page fault. With that
in mind, change over to calling get_user_pages_fast(). This simplifies
the code, runs a little faster in the expected case, and allows removing
get_user_pages_locked() entirely, in a subsequent patch.
Link: https://lkml.kernel.org/r/20220204020010.68930-5-jhubbard@xxxxxxxxxx
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mempolicy.c | 21 +++++++++------------
1 file changed, 9 insertions(+), 12 deletions(-)
--- a/mm/mempolicy.c~mm-change-lookup_node-to-use-get_user_pages_fast
+++ a/mm/mempolicy.c
@@ -907,17 +907,14 @@ static void get_policy_nodemask(struct m
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);
+ ret = get_user_pages_fast(addr & PAGE_MASK, 1, 0, &p);
+ if (ret > 0) {
+ ret = page_to_nid(p);
put_page(p);
}
- if (locked)
- mmap_read_unlock(mm);
- return err;
+ return ret;
}
/* Retrieve NUMA policy */
@@ -968,14 +965,14 @@ static long do_get_mempolicy(int *policy
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);
+ mmap_read_unlock(mm);
err = lookup_node(mm, addr);
if (err < 0)
goto out;
_
Patches currently in -mm which might be from jhubbard@xxxxxxxxxx are
