The patch titled
Subject: mm: gup: pack has_pinned in MMF_HAS_PINNED
has been added to the -mm tree. Its filename is
mm-gup-pack-has_pinned-in-mmf_has_pinned.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-gup-pack-has_pinned-in-mmf_has_pinned.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-gup-pack-has_pinned-in-mmf_has_pinned.patch
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------------------------------------------------------
From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Subject: mm: gup: pack has_pinned in MMF_HAS_PINNED
has_pinned 32bit can be packed in the MMF_HAS_PINNED bit as a noop
cleanup.
Any atomic_inc/dec to the mm cacheline shared by all threads in pin-fast
would reintroduce a loss of SMP scalability to pin-fast, so there's no
future potential usefulness to keep an atomic in the mm for this.
set_bit(MMF_HAS_PINNED) will be theoretically a bit slower than WRITE_ONCE
(atomic_set is equivalent to WRITE_ONCE), but the set_bit (just like
atomic_set after this commit) has to be still issued only once per "mm",
so the difference between the two will be lost in the noise.
will-it-scale "mmap2" shows no change in performance with enterprise
config as expected.
will-it-scale "pin_fast" retains the > 4000% SMP scalability performance
improvement against upstream as expected.
This is a noop as far as overall performance and SMP scalability are
concerned.
[peterx@xxxxxxxxxx: fix build for task_mmu.c, introduce mm_set_has_pinned_flag, fix comments]
Link: https://lkml.kernel.org/r/20210507150553.208763-4-peterx@xxxxxxxxxx
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Kirill Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/task_mmu.c | 2 +-
include/linux/mm.h | 2 +-
include/linux/mm_types.h | 10 ----------
include/linux/sched/coredump.h | 8 ++++++++
kernel/fork.c | 1 -
mm/gup.c | 19 +++++++++++++++----
6 files changed, 25 insertions(+), 17 deletions(-)
--- a/fs/proc/task_mmu.c~mm-gup-pack-has_pinned-in-mmf_has_pinned
+++ a/fs/proc/task_mmu.c
@@ -1047,7 +1047,7 @@ static inline bool pte_is_pinned(struct
return false;
if (!is_cow_mapping(vma->vm_flags))
return false;
- if (likely(!atomic_read(&vma->vm_mm->has_pinned)))
+ if (likely(!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags)))
return false;
page = vm_normal_page(vma, addr, pte);
if (!page)
--- a/include/linux/mm.h~mm-gup-pack-has_pinned-in-mmf_has_pinned
+++ a/include/linux/mm.h
@@ -1341,7 +1341,7 @@ static inline bool page_needs_cow_for_dm
if (!is_cow_mapping(vma->vm_flags))
return false;
- if (!atomic_read(&vma->vm_mm->has_pinned))
+ if (!test_bit(MMF_HAS_PINNED, &vma->vm_mm->flags))
return false;
return page_maybe_dma_pinned(page);
--- a/include/linux/mm_types.h~mm-gup-pack-has_pinned-in-mmf_has_pinned
+++ a/include/linux/mm_types.h
@@ -436,16 +436,6 @@ struct mm_struct {
atomic_t mm_count;
/**
- * @has_pinned: Whether this mm has pinned any pages. This can
- * be either replaced in the future by @pinned_vm when it
- * becomes stable, or grow into a counter on its own. We're
- * aggresive on this bit now - even if the pinned pages were
- * unpinned later on, we'll still keep this bit set for the
- * lifecycle of this mm just for simplicity.
- */
- atomic_t has_pinned;
-
- /**
* @write_protect_seq: Locked when any thread is write
* protecting pages mapped by this mm to enforce a later COW,
* for instance during page table copying for fork().
--- a/include/linux/sched/coredump.h~mm-gup-pack-has_pinned-in-mmf_has_pinned
+++ a/include/linux/sched/coredump.h
@@ -73,6 +73,14 @@ static inline int get_dumpable(struct mm
#define MMF_OOM_VICTIM 25 /* mm is the oom victim */
#define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */
#define MMF_MULTIPROCESS 27 /* mm is shared between processes */
+/*
+ * MMF_HAS_PINNED: Whether this mm has pinned any pages. This can be either
+ * replaced in the future by mm.pinned_vm when it becomes stable, or grow into
+ * a counter on its own. We're aggresive on this bit for now: even if the
+ * pinned pages were unpinned later on, we'll still keep this bit set for the
+ * lifecycle of this mm, just for simplicity.
+ */
+#define MMF_HAS_PINNED 28 /* FOLL_PIN has run, never cleared */
#define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP)
#define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\
--- a/kernel/fork.c~mm-gup-pack-has_pinned-in-mmf_has_pinned
+++ a/kernel/fork.c
@@ -1029,7 +1029,6 @@ static struct mm_struct *mm_init(struct
mm_pgtables_bytes_init(mm);
mm->map_count = 0;
mm->locked_vm = 0;
- atomic_set(&mm->has_pinned, 0);
atomic64_set(&mm->pinned_vm, 0);
memset(&mm->rss_stat, 0, sizeof(mm->rss_stat));
spin_lock_init(&mm->page_table_lock);
--- a/mm/gup.c~mm-gup-pack-has_pinned-in-mmf_has_pinned
+++ a/mm/gup.c
@@ -1271,6 +1271,17 @@ retry:
EXPORT_SYMBOL_GPL(fixup_user_fault);
/*
+ * Set the MMF_HAS_PINNED if not set yet; after set it'll be there for the mm's
+ * lifecycle. Avoid setting the bit unless necessary, or it might cause write
+ * cache bouncing on large SMP machines for concurrent pinned gups.
+ */
+static inline void mm_set_has_pinned_flag(unsigned long *mm_flags)
+{
+ if (!test_bit(MMF_HAS_PINNED, mm_flags))
+ set_bit(MMF_HAS_PINNED, mm_flags);
+}
+
+/*
* Please note that this function, unlike __get_user_pages will not
* return 0 for nr_pages > 0 without FOLL_NOWAIT
*/
@@ -1292,8 +1303,8 @@ static __always_inline long __get_user_p
BUG_ON(*locked != 1);
}
- if ((flags & FOLL_PIN) && !atomic_read(&mm->has_pinned))
- atomic_set(&mm->has_pinned, 1);
+ if (flags & FOLL_PIN)
+ mm_set_has_pinned_flag(&mm->flags);
/*
* FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior
@@ -2613,8 +2624,8 @@ static int internal_get_user_pages_fast(
FOLL_FAST_ONLY)))
return -EINVAL;
- if ((gup_flags & FOLL_PIN) && !atomic_read(¤t->mm->has_pinned))
- atomic_set(¤t->mm->has_pinned, 1);
+ if (gup_flags & FOLL_PIN)
+ mm_set_has_pinned_flag(¤t->mm->flags);
if (!(gup_flags & FOLL_FAST_ONLY))
might_lock_read(¤t->mm->mmap_lock);
_
Patches currently in -mm which might be from aarcange@xxxxxxxxxx are
mm-gup-allow-foll_pin-to-scale-in-smp.patch
mm-gup-pack-has_pinned-in-mmf_has_pinned.patch
