[RFC][PATCH v2 6/8] wipe_page_reference return SWAP_AGAIN if VM pressulre is low and lock contention is detected.

KOSAKI Motohiro
2009-12-10T07:33:35Z

Larry Woodman reported AIM7 makes serious ptelock and anon_vma_lock
contention on current VM. because SplitLRU VM (since 2.6.28) remove
calc_reclaim_mapped() test, then shrink_active_list() always call
page_referenced() against mapped page although VM pressure is low.
Lightweight VM pressure is very common situation and it easily makes
ptelock contention with page fault. then, anon_vma_lock is holding
long time and it makes another lock contention. then, fork/exit
throughput decrease a lot.

While running workloads that do lots of forking processes, exiting
processes and page reclamation(AIM 7) on large systems very high system
time(100%) and lots of lock contention was observed.

CPU5:
[<ffffffff814afb48>] ? _spin_lock+0x27/0x48
[<ffffffff81101deb>] ? anon_vma_link+0x2a/0x5a
[<ffffffff8105d3d8>] ? dup_mm+0x242/0x40c
[<ffffffff8105e0a9>] ? copy_process+0xab1/0x12be
[<ffffffff8105ea07>] ? do_fork+0x151/0x330
[<ffffffff81058407>] ? default_wake_function+0x0/0x36
[<ffffffff814b0243>] ? _spin_lock_irqsave+0x2f/0x68
[<ffffffff810121d3>] ? stub_clone+0x13/0x20
[<ffffffff81011e02>] ? system_call_fastpath+0x16/0x1b

CPU4:
[<ffffffff814afb4a>] ? _spin_lock+0x29/0x48
[<ffffffff81103062>] ? anon_vma_unlink+0x2a/0x84
[<ffffffff810fbab7>] ? free_pgtables+0x3c/0xe1
[<ffffffff810fd8b1>] ? exit_mmap+0xc5/0x110
[<ffffffff8105ce4c>] ? mmput+0x55/0xd9
[<ffffffff81061afd>] ? exit_mm+0x109/0x129
[<ffffffff81063846>] ? do_exit+0x1d7/0x712
[<ffffffff814b0243>] ? _spin_lock_irqsave+0x2f/0x68
[<ffffffff81063e07>] ? do_group_exit+0x86/0xb2
[<ffffffff81063e55>] ? sys_exit_group+0x22/0x3e
[<ffffffff81011e02>] ? system_call_fastpath+0x16/0x1b

CPU0:
[<ffffffff814afb4a>] ? _spin_lock+0x29/0x48
[<ffffffff81101ad1>] ? page_check_address+0x9e/0x16f
[<ffffffff81101cb8>] ? page_referenced_one+0x53/0x10b
[<ffffffff81102f5a>] ? page_referenced+0xcd/0x167
[<ffffffff810eb32d>] ? shrink_active_list+0x1ed/0x2a3
[<ffffffff810ebde9>] ? shrink_zone+0xa06/0xa38
[<ffffffff8108440a>] ? getnstimeofday+0x64/0xce
[<ffffffff810ecaf9>] ? do_try_to_free_pages+0x1e5/0x362
[<ffffffff810ecd9f>] ? try_to_free_pages+0x7a/0x94
[<ffffffff810ea66f>] ? isolate_pages_global+0x0/0x242
[<ffffffff810e57b9>] ? __alloc_pages_nodemask+0x397/0x572
[<ffffffff810e3c1e>] ? __get_free_pages+0x19/0x6e
[<ffffffff8105d6c9>] ? copy_process+0xd1/0x12be
[<ffffffff81204eb2>] ? avc_has_perm+0x5c/0x84
[<ffffffff81130db8>] ? user_path_at+0x65/0xa3
[<ffffffff8105ea07>] ? do_fork+0x151/0x330
[<ffffffff810b7935>] ? check_for_new_grace_period+0x78/0xab
[<ffffffff810121d3>] ? stub_clone+0x13/0x20
[<ffffffff81011e02>] ? system_call_fastpath+0x16/0x1b

------------------------------------------------------------------------------
PerfTop: 864 irqs/sec kernel:99.7% [100000 cycles], (all, 8 CPUs)
------------------------------------------------------------------------------

samples pcnt RIP kernel function
______ _______ _____ ________________ _______________

3235.00 - 75.1% - ffffffff814afb21 : _spin_lock
670.00 - 15.6% - ffffffff81101a33 : page_check_address
165.00 - 3.8% - ffffffffa01cbc39 : rpc_sleep_on [sunrpc]
40.00 - 0.9% - ffffffff81102113 : try_to_unmap_one
29.00 - 0.7% - ffffffff81101c65 : page_referenced_one
27.00 - 0.6% - ffffffff81101964 : vma_address
8.00 - 0.2% - ffffffff8125a5a0 : clear_page_c
6.00 - 0.1% - ffffffff8125a5f0 : copy_page_c
6.00 - 0.1% - ffffffff811023ca : try_to_unmap_anon
5.00 - 0.1% - ffffffff810fb014 : copy_page_range
5.00 - 0.1% - ffffffff810e4d18 : get_page_from_freelist

Then, We use trylock for avoiding ptelock contention if VM pressure is
low.

Reported-by: Larry Woodman <lwoodman@redhat.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: Rik van Riel <riel@redhat.com>
---
include/linux/rmap.h | 4 ++++
mm/rmap.c | 16 ++++++++++++----
mm/vmscan.c | 1 +
3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 564d981..499972e 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -110,6 +110,10 @@ static inline void page_dup_rmap(struct page *page)

struct page_reference_context {
int is_page_locked;
+
+ /* if 1, we might give up to wipe when find lock contention. */
+ int soft_try;
+
unsigned long referenced;
unsigned long exec_referenced;
int maybe_mlocked; /* found VM_LOCKED, but it's unstable result */
diff --git a/mm/rmap.c b/mm/rmap.c
index b84f350..5ae7c81 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -373,6 +373,9 @@ int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
/*
* Subfunctions of wipe_page_reference: wipe_page_reference_one called
* repeatedly from either wipe_page_reference_anon or wipe_page_reference_file.
+ *
+ * SWAP_SUCCESS - success
+ * SWAP_AGAIN - give up to take lock, try later again
*/
int wipe_page_reference_one(struct page *page,
struct page_reference_context *refctx,
@@ -381,6 +384,7 @@ int wipe_page_reference_one(struct page *page,
struct mm_struct *mm = vma->vm_mm;
pte_t *pte;
spinlock_t *ptl;
+ int ret = SWAP_SUCCESS;

/*
* Don't want to elevate referenced for mlocked page that gets this far,
@@ -392,10 +396,14 @@ int wipe_page_reference_one(struct page *page,
goto out;
}

- pte = page_check_address(page, mm, address, &ptl, 0);
- if (!pte)
+ pte = __page_check_address(page, mm, address, &ptl, 0,
+ refctx->soft_try);
+ if (IS_ERR(pte)) {
+ if (PTR_ERR(pte) == -EAGAIN) {
+ ret = SWAP_AGAIN;
+ }
goto out;
-
+ }
if (ptep_clear_flush_young_notify(vma, address, pte)) {
/*
* Don't treat a reference through a sequentially read
@@ -421,7 +429,7 @@ int wipe_page_reference_one(struct page *page,
pte_unmap_unlock(pte, ptl);

out:
- return SWAP_SUCCESS;
+ return ret;
}

static int wipe_page_reference_anon(struct page *page,
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a01cf5e..c235059 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1329,6 +1329,7 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
int ret;
struct page_reference_context refctx = {
.is_page_locked = 0,
+ .soft_try = (priority < DEF_PRIORITY - 2) ? 0 : 1,
};

cond_resched();