[PATCH v2 31/35] mm: anon spf statistics

From: Michel Lespinasse
Date: Fri Jan 28 2022 - 08:20:38 EST

Next message: Michel Lespinasse: "[PATCH v2 34/35] powerpc/mm: define ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT"
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Add a new CONFIG_SPECULATIVE_PAGE_FAULT_STATS config option,
and dump extra statistics about executed spf cases and abort reasons
when the option is set.

Signed-off-by: Michel Lespinasse <michel@xxxxxxxxxxxxxx>
---
arch/x86/mm/fault.c | 18 ++++++++---
include/linux/mmap_lock.h | 19 ++++++++++--
include/linux/vm_event.h | 6 ++++
include/linux/vm_event_item.h | 21 +++++++++++++
mm/Kconfig.debug | 7 +++++
mm/memory.c | 56 ++++++++++++++++++++++++++++-------
mm/vmstat.c | 21 +++++++++++++
7 files changed, 131 insertions(+), 17 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index d6f8d4967c49..a5a19561c319 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1337,21 +1337,31 @@ void do_user_addr_fault(struct pt_regs *regs,

count_vm_event(SPF_ATTEMPT);
seq = mmap_seq_read_start(mm);
- if (seq & 1)
+ if (seq & 1) {
+ count_vm_spf_event(SPF_ABORT_ODD);
goto spf_abort;
+ }
rcu_read_lock();
vma = __find_vma(mm, address);
- if (!vma || vma->vm_start > address || !vma_is_anonymous(vma)) {
+ if (!vma || vma->vm_start > address) {
rcu_read_unlock();
+ count_vm_spf_event(SPF_ABORT_UNMAPPED);
+ goto spf_abort;
+ }
+ if (!vma_is_anonymous(vma)) {
+ rcu_read_unlock();
+ count_vm_spf_event(SPF_ABORT_NO_SPECULATE);
goto spf_abort;
}
pvma = *vma;
rcu_read_unlock();
- if (!mmap_seq_read_check(mm, seq))
+ if (!mmap_seq_read_check(mm, seq, SPF_ABORT_VMA_COPY))
goto spf_abort;
vma = &pvma;
- if (unlikely(access_error(error_code, vma)))
+ if (unlikely(access_error(error_code, vma))) {
+ count_vm_spf_event(SPF_ABORT_ACCESS_ERROR);
goto spf_abort;
+ }
fault = do_handle_mm_fault(vma, address,
flags | FAULT_FLAG_SPECULATIVE, seq, regs);

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index a2459eb15a33..747805ce07b8 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -7,6 +7,7 @@
#include <linux/rwsem.h>
#include <linux/tracepoint-defs.h>
#include <linux/types.h>
+#include <linux/vm_event.h>

#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
#define MMAP_LOCK_SEQ_INITIALIZER(name) \
@@ -104,12 +105,26 @@ static inline unsigned long mmap_seq_read_start(struct mm_struct *mm)
return seq;
}

-static inline bool mmap_seq_read_check(struct mm_struct *mm, unsigned long seq)
+static inline bool __mmap_seq_read_check(struct mm_struct *mm,
+ unsigned long seq)
{
smp_rmb();
return seq == READ_ONCE(mm->mmap_seq);
}
-#endif
+
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT_STATS
+static inline bool mmap_seq_read_check(struct mm_struct *mm, unsigned long seq,
+ enum vm_event_item fail_event)
+{
+ if (__mmap_seq_read_check(mm, seq))
+ return true;
+ count_vm_event(fail_event);
+ return false;
+}
+#else
+#define mmap_seq_read_check(mm, seq, fail) __mmap_seq_read_check(mm, seq)
+#endif /* CONFIG_SPECULATIVE_PAGE_FAULT_STATS */
+#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */

static inline void mmap_write_lock(struct mm_struct *mm)
{
diff --git a/include/linux/vm_event.h b/include/linux/vm_event.h
index b3ae108a3841..689a21387dad 100644
--- a/include/linux/vm_event.h
+++ b/include/linux/vm_event.h
@@ -77,6 +77,12 @@ static inline void vm_events_fold_cpu(int cpu)

#endif /* CONFIG_VM_EVENT_COUNTERS */

+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT_STATS
+#define count_vm_spf_event(x) count_vm_event(x)
+#else
+#define count_vm_spf_event(x) do {} while (0)
+#endif
+
#ifdef CONFIG_NUMA_BALANCING
#define count_vm_numa_event(x) count_vm_event(x)
#define count_vm_numa_events(x, y) count_vm_events(x, y)
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index f00b3e36ff39..0390b81b1e71 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -137,6 +137,27 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
SPF_ATTEMPT,
SPF_ABORT,
+#endif
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT_STATS
+ SPF_ABORT_ODD,
+ SPF_ABORT_UNMAPPED,
+ SPF_ABORT_NO_SPECULATE,
+ SPF_ABORT_VMA_COPY,
+ SPF_ABORT_ACCESS_ERROR,
+ SPF_ABORT_PUD,
+ SPF_ABORT_PMD,
+ SPF_ABORT_ANON_VMA,
+ SPF_ABORT_PTE_MAP_LOCK_SEQ1,
+ SPF_ABORT_PTE_MAP_LOCK_PMD,
+ SPF_ABORT_PTE_MAP_LOCK_PTL,
+ SPF_ABORT_PTE_MAP_LOCK_SEQ2,
+ SPF_ABORT_USERFAULTFD,
+ SPF_ABORT_FAULT,
+ SPF_ABORT_SWAP,
+ SPF_ATTEMPT_ANON,
+ SPF_ATTEMPT_NUMA,
+ SPF_ATTEMPT_PTE,
+ SPF_ATTEMPT_WP,
#endif
NR_VM_EVENT_ITEMS
};
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 5bd5bb097252..73b61cc95562 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -174,3 +174,10 @@ config PTDUMP_DEBUGFS
kernel.

If in doubt, say N.
+
+config SPECULATIVE_PAGE_FAULT_STATS
+ bool "Additional statistics for speculative page faults"
+ depends on SPECULATIVE_PAGE_FAULT
+ help
+ Additional statistics for speculative page faults.
+ If in doubt, say N.
diff --git a/mm/memory.c b/mm/memory.c
index 7f8dbd729dce..a5754309eaae 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2762,7 +2762,8 @@ bool __pte_map_lock(struct vm_fault *vmf)
}

speculative_page_walk_begin();
- if (!mmap_seq_read_check(vmf->vma->vm_mm, vmf->seq))
+ if (!mmap_seq_read_check(vmf->vma->vm_mm, vmf->seq,
+ SPF_ABORT_PTE_MAP_LOCK_SEQ1))
goto fail;
/*
* The mmap sequence count check guarantees that the page
@@ -2775,8 +2776,10 @@ bool __pte_map_lock(struct vm_fault *vmf)
* is not a huge collapse operation in progress in our back.
*/
pmdval = READ_ONCE(*vmf->pmd);
- if (!pmd_same(pmdval, vmf->orig_pmd))
+ if (!pmd_same(pmdval, vmf->orig_pmd)) {
+ count_vm_spf_event(SPF_ABORT_PTE_MAP_LOCK_PMD);
goto fail;
+ }
#endif
ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
if (!pte)
@@ -2793,9 +2796,12 @@ bool __pte_map_lock(struct vm_fault *vmf)
* We also don't want to retry until spin_trylock() succeeds,
* because of the starvation potential against a stream of lockers.
*/
- if (unlikely(!spin_trylock(ptl)))
+ if (unlikely(!spin_trylock(ptl))) {
+ count_vm_spf_event(SPF_ABORT_PTE_MAP_LOCK_PTL);
goto fail;
- if (!mmap_seq_read_check(vmf->vma->vm_mm, vmf->seq))
+ }
+ if (!mmap_seq_read_check(vmf->vma->vm_mm, vmf->seq,
+ SPF_ABORT_PTE_MAP_LOCK_SEQ2))
goto unlock_fail;
speculative_page_walk_end();
vmf->pte = pte;
@@ -3091,6 +3097,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)

if (unlikely(!vma->anon_vma)) {
if (vmf->flags & FAULT_FLAG_SPECULATIVE) {
+ count_vm_spf_event(SPF_ABORT_ANON_VMA);
ret = VM_FAULT_RETRY;
goto out;
}
@@ -3367,10 +3374,15 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;

+ if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+ count_vm_spf_event(SPF_ATTEMPT_WP);
+
if (userfaultfd_pte_wp(vma, *vmf->pte)) {
pte_unmap_unlock(vmf->pte, vmf->ptl);
- if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+ if (vmf->flags & FAULT_FLAG_SPECULATIVE) {
+ count_vm_spf_event(SPF_ABORT_USERFAULTFD);
return VM_FAULT_RETRY;
+ }
return handle_userfault(vmf, VM_UFFD_WP);
}

@@ -3620,6 +3632,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)

if (vmf->flags & FAULT_FLAG_SPECULATIVE) {
pte_unmap(vmf->pte);
+ count_vm_spf_event(SPF_ABORT_SWAP);
return VM_FAULT_RETRY;
}

@@ -3852,6 +3865,9 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
vm_fault_t ret = 0;
pte_t entry;

+ if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+ count_vm_spf_event(SPF_ATTEMPT_ANON);
+
/* File mapping without ->vm_ops ? */
if (vma->vm_flags & VM_SHARED)
return VM_FAULT_SIGBUS;
@@ -3881,8 +3897,10 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
} else {
/* Allocate our own private page. */
if (unlikely(!vma->anon_vma)) {
- if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+ if (vmf->flags & FAULT_FLAG_SPECULATIVE) {
+ count_vm_spf_event(SPF_ABORT_ANON_VMA);
return VM_FAULT_RETRY;
+ }
if (__anon_vma_prepare(vma))
goto oom;
}
@@ -3925,8 +3943,10 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
pte_unmap_unlock(vmf->pte, vmf->ptl);
if (page)
put_page(page);
- if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+ if (vmf->flags & FAULT_FLAG_SPECULATIVE) {
+ count_vm_spf_event(SPF_ABORT_USERFAULTFD);
return VM_FAULT_RETRY;
+ }
return handle_userfault(vmf, VM_UFFD_MISSING);
}

@@ -4470,6 +4490,9 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
bool was_writable = pte_savedwrite(vmf->orig_pte);
int flags = 0;

+ if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+ count_vm_spf_event(SPF_ATTEMPT_NUMA);
+
/*
* The "pte" at this point cannot be used safely without
* validation through pte_unmap_same(). It's of NUMA type but
@@ -4651,6 +4674,9 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma))
return do_numa_page(vmf);

+ if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+ count_vm_spf_event(SPF_ATTEMPT_PTE);
+
if (!pte_spinlock(vmf))
return VM_FAULT_RETRY;
entry = vmf->orig_pte;
@@ -4718,20 +4744,26 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
speculative_page_walk_begin();
pgd = pgd_offset(mm, address);
pgdval = READ_ONCE(*pgd);
- if (pgd_none(pgdval) || unlikely(pgd_bad(pgdval)))
+ if (pgd_none(pgdval) || unlikely(pgd_bad(pgdval))) {
+ count_vm_spf_event(SPF_ABORT_PUD);
goto spf_fail;
+ }

p4d = p4d_offset(pgd, address);
p4dval = READ_ONCE(*p4d);
- if (p4d_none(p4dval) || unlikely(p4d_bad(p4dval)))
+ if (p4d_none(p4dval) || unlikely(p4d_bad(p4dval))) {
+ count_vm_spf_event(SPF_ABORT_PUD);
goto spf_fail;
+ }

vmf.pud = pud_offset(p4d, address);
pudval = READ_ONCE(*vmf.pud);
if (pud_none(pudval) || unlikely(pud_bad(pudval)) ||
unlikely(pud_trans_huge(pudval)) ||
- unlikely(pud_devmap(pudval)))
+ unlikely(pud_devmap(pudval))) {
+ count_vm_spf_event(SPF_ABORT_PUD);
goto spf_fail;
+ }

vmf.pmd = pmd_offset(vmf.pud, address);
vmf.orig_pmd = READ_ONCE(*vmf.pmd);
@@ -4749,8 +4781,10 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
if (unlikely(pmd_none(vmf.orig_pmd) ||
is_swap_pmd(vmf.orig_pmd) ||
pmd_trans_huge(vmf.orig_pmd) ||
- pmd_devmap(vmf.orig_pmd)))
+ pmd_devmap(vmf.orig_pmd))) {
+ count_vm_spf_event(SPF_ABORT_PMD);
goto spf_fail;
+ }

/*
* The above does not allocate/instantiate page-tables because
diff --git a/mm/vmstat.c b/mm/vmstat.c
index dbb0160e5558..20ac17cf582a 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1394,6 +1394,27 @@ const char * const vmstat_text[] = {
"spf_attempt",
"spf_abort",
#endif
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT_STATS
+ "SPF_ABORT_ODD",
+ "SPF_ABORT_UNMAPPED",
+ "SPF_ABORT_NO_SPECULATE",
+ "SPF_ABORT_VMA_COPY",
+ "SPF_ABORT_ACCESS_ERROR",
+ "SPF_ABORT_PUD",
+ "SPF_ABORT_PMD",
+ "SPF_ABORT_ANON_VMA",
+ "SPF_ABORT_PTE_MAP_LOCK_SEQ1",
+ "SPF_ABORT_PTE_MAP_LOCK_PMD",
+ "SPF_ABORT_PTE_MAP_LOCK_PTL",
+ "SPF_ABORT_PTE_MAP_LOCK_SEQ2",
+ "SPF_ABORT_USERFAULTFD",
+ "SPF_ABORT_FAULT",
+ "SPF_ABORT_SWAP",
+ "SPF_ATTEMPT_ANON",
+ "SPF_ATTEMPT_NUMA",
+ "SPF_ATTEMPT_PTE",
+ "SPF_ATTEMPT_WP",
+#endif
#endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */
};
#endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */
--
2.20.1

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