Hi Peter, Jason and all,
Changes since v2:
* Patch 2: Removed an unnecessary line that was causing a
clang-analyzer complaint, as reported by Lukas Bulwahn
[1] (thanks!), and retested locally.
Jason: I've boldly left your Reviewed-by tag on this patch,
because I am predicting you'll agree with it...
* Added Reviewed-by tags from Jan Kara, Christoph Hellwig, and
Jason Gunthorpe that have collected since v2.
Changes since v1:
* Patch 4: changed from get_user_pages(), to get_user_pages_fast().
* Patch 4: Rewrote the commit description--thanks to Jan Kara for
that feedback.
* Patch 1: Removed Jerome's Cc from patch 1, due to a stale email
address.
* Added Reviewed-by's from David Hildenbrand and Jason Gunthorpe.
Original cover letter, updated as necessary:
I'm including Peter's patch as the first one in this tiny series. (The
commit description has my r-b tag in place of my Cc, and removes
Jerome's Cc because he is no longer at redhat.com) The second patch is
what I had in mind for a follow-up to that, when we were discussing that
fix [2].
Plus, a couple more small removals that I had queued up:
The third patch removes a completely unused routine:
pin_user_pages_locked().
The forth patch removes a similar routine, get_user_pages_locked(), that
only has one caller. It now calls get_user_pages_fast(), instead.
v1 of this patchset is here:
https://lore.kernel.org/all/[email protected]/
v2 of this patchset is here:
https://lore.kernel.org/r/[email protected]
[1] https://lore.kernel.org/r/CAKXUXMxFK9bo8jDoRZbQ0r2j-JwAGg3Xc5cpAcLaHfwHddJ7ew@mail.gmail.com
[2] https://lore.kernel.org/all/[email protected]/
thanks,
John Hubbard
John Hubbard (3):
mm/gup: clean up follow_pfn_pte() slightly
mm/gup: remove unused pin_user_pages_locked()
mm/gup: remove get_user_pages_locked()
Peter Xu (1):
mm: Fix invalid page pointer returned with FOLL_PIN gups
include/linux/mm.h | 4 --
mm/gup.c | 99 +++-------------------------------------------
mm/mempolicy.c | 21 +++++-----
3 files changed, 15 insertions(+), 109 deletions(-)
base-commit: 88808fbbead481aedb46640a5ace69c58287f56a
--
2.35.1
There is only one caller of get_user_pages_locked(). The purpose of
get_user_pages_locked() is 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 is 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.
Reviewed-by: Jan Kara <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Signed-off-by: John Hubbard <[email protected]>
---
include/linux/mm.h | 2 --
mm/gup.c | 59 ----------------------------------------------
mm/mempolicy.c | 21 +++++++----------
3 files changed, 9 insertions(+), 73 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 80c540c17d83..528ef1cb4f3a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1916,8 +1916,6 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
long pin_user_pages(unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas);
-long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
- unsigned int gup_flags, struct page **pages, int *locked);
long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
struct page **pages, unsigned int gup_flags);
long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
diff --git a/mm/gup.c b/mm/gup.c
index b0ecbfe03928..7da49df59110 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2118,65 +2118,6 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
}
EXPORT_SYMBOL(get_user_pages);
-/**
- * get_user_pages_locked() - variant of get_user_pages()
- *
- * @start: starting user address
- * @nr_pages: number of pages from start to pin
- * @gup_flags: flags modifying lookup behaviour
- * @pages: array that receives pointers to the pages pinned.
- * Should be at least nr_pages long. Or NULL, if caller
- * only intends to ensure the pages are faulted in.
- * @locked: pointer to lock flag indicating whether lock is held and
- * subsequently whether VM_FAULT_RETRY functionality can be
- * utilised. Lock must initially be held.
- *
- * It is suitable to replace the form:
- *
- * mmap_read_lock(mm);
- * do_something()
- * get_user_pages(mm, ..., pages, NULL);
- * mmap_read_unlock(mm);
- *
- * to:
- *
- * int locked = 1;
- * mmap_read_lock(mm);
- * do_something()
- * get_user_pages_locked(mm, ..., pages, &locked);
- * if (locked)
- * mmap_read_unlock(mm);
- *
- * We can leverage the VM_FAULT_RETRY functionality in the page fault
- * paths better by using either get_user_pages_locked() or
- * get_user_pages_unlocked().
- *
- */
-long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
- unsigned int gup_flags, struct page **pages,
- int *locked)
-{
- /*
- * FIXME: Current FOLL_LONGTERM behavior is incompatible with
- * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
- * vmas. As there are no users of this flag in this call we simply
- * disallow this option for now.
- */
- if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
- return -EINVAL;
- /*
- * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
- * never directly by the caller, so enforce that:
- */
- if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
- return -EINVAL;
-
- return __get_user_pages_locked(current->mm, start, nr_pages,
- pages, NULL, locked,
- gup_flags | FOLL_TOUCH);
-}
-EXPORT_SYMBOL(get_user_pages_locked);
-
/*
* get_user_pages_unlocked() is suitable to replace the form:
*
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 028e8dd82b44..3f8dc58da3e8 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -907,17 +907,14 @@ 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);
+ 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, 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);
+ mmap_read_unlock(mm);
err = lookup_node(mm, addr);
if (err < 0)
goto out;
--
2.35.1
On Thu, Feb 03, 2022 at 01:32:32AM -0800, John Hubbard wrote:
> There is only one caller of get_user_pages_locked(). The purpose of
> get_user_pages_locked() is 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 is 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.
Maybe split the lookup_node changes into a separate patch, as that
allows to document that change even better.
On 2/3/22 06:01, Christoph Hellwig wrote:
> On Thu, Feb 03, 2022 at 01:32:32AM -0800, John Hubbard wrote:
>> There is only one caller of get_user_pages_locked(). The purpose of
>> get_user_pages_locked() is 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 is 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.
>
> Maybe split the lookup_node changes into a separate patch, as that
> allows to document that change even better.
OK, I'll do that.
thanks,
--
John Hubbard
NVIDIA