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Date: Fri, 18 Feb 2022 13:20:19 +0100
From: Jakub Matěna <matenajakub@...il.com>
To: linux-mm@...ck.org
Cc: patches@...ts.linux.dev, linux-kernel@...r.kernel.org,
vbabka@...e.cz, mhocko@...nel.org, mgorman@...hsingularity.net,
willy@...radead.org, liam.howlett@...cle.com, hughd@...gle.com,
kirill@...temov.name, riel@...riel.com, rostedt@...dmis.org,
peterz@...radead.org,
Jakub Matěna <matenajakub@...il.com>
Subject: [RFC PATCH 4/4] [PATCH 4/4] mm: add tracing for VMA merges
Adds trace support for vma_merge to measure successful and unsuccessful
merges of two VMAs with distinct anon_vmas and also trace support for
merges made possible by update of page offset made possible by a previous
patch in this series.
Signed-off-by: Jakub Matěna <matenajakub@...il.com>
---
include/trace/events/mmap.h | 55 ++++++++++++++++++++++++++++++++
mm/internal.h | 11 +++++++
mm/mmap.c | 63 ++++++++++++++++++++-----------------
3 files changed, 100 insertions(+), 29 deletions(-)
diff --git a/include/trace/events/mmap.h b/include/trace/events/mmap.h
index 4661f7ba07c0..9f6439e2ed2d 100644
--- a/include/trace/events/mmap.h
+++ b/include/trace/events/mmap.h
@@ -6,6 +6,7 @@
#define _TRACE_MMAP_H
#include <linux/tracepoint.h>
+#include <../mm/internal.h>
TRACE_EVENT(vm_unmapped_area,
@@ -42,6 +43,60 @@ TRACE_EVENT(vm_unmapped_area,
__entry->low_limit, __entry->high_limit, __entry->align_mask,
__entry->align_offset)
);
+
+TRACE_EVENT(vm_av_merge,
+
+ TP_PROTO(int merged, enum vma_merge_res merge_prev, enum vma_merge_res merge_next, enum vma_merge_res merge_both),
+
+ TP_ARGS(merged, merge_prev, merge_next, merge_both),
+
+ TP_STRUCT__entry(
+ __field(int, merged)
+ __field(enum vma_merge_res, predecessor_different_av)
+ __field(enum vma_merge_res, successor_different_av)
+ __field(enum vma_merge_res, predecessor_with_successor_different_av)
+ __field(int, diff_count)
+ __field(int, failed_count)
+ ),
+
+ TP_fast_assign(
+ __entry->merged = merged == 0;
+ __entry->predecessor_different_av = merge_prev;
+ __entry->successor_different_av = merge_next;
+ __entry->predecessor_with_successor_different_av = merge_both;
+ __entry->diff_count = (merge_prev == AV_MERGE_DIFFERENT)
+ + (merge_next == AV_MERGE_DIFFERENT) + (merge_both == AV_MERGE_DIFFERENT);
+ __entry->failed_count = (merge_prev == AV_MERGE_FAILED)
+ + (merge_next == AV_MERGE_FAILED) + (merge_both == AV_MERGE_FAILED);
+ ),
+
+ TP_printk("merged=%d predecessor=%d successor=%d predecessor_with_successor=%d diff_count=%d failed_count=%d\n",
+ __entry->merged,
+ __entry->predecessor_different_av, __entry->successor_different_av,
+ __entry->predecessor_with_successor_different_av,
+ __entry->diff_count, __entry->failed_count)
+
+);
+
+TRACE_EVENT(vm_pgoff_merge,
+
+ TP_PROTO(struct vm_area_struct *vma, bool anon_pgoff_updated),
+
+ TP_ARGS(vma, anon_pgoff_updated),
+
+ TP_STRUCT__entry(
+ __field(bool, faulted)
+ __field(bool, updated)
+ ),
+
+ TP_fast_assign(
+ __entry->faulted = vma->anon_vma;
+ __entry->updated = anon_pgoff_updated;
+ ),
+
+ TP_printk("faulted=%d updated=%d\n",
+ __entry->faulted, __entry->updated)
+);
#endif
/* This part must be outside protection */
diff --git a/mm/internal.h b/mm/internal.h
index d80300392a19..b3e482175518 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -34,6 +34,17 @@ struct folio_batch;
/* Do not use these with a slab allocator */
#define GFP_SLAB_BUG_MASK (__GFP_DMA32|__GFP_HIGHMEM|~__GFP_BITS_MASK)
+/*
+ * Following values indicate reason for merge success or failure.
+ */
+enum vma_merge_res {
+ MERGE_FAILED,
+ AV_MERGE_FAILED,
+ AV_MERGE_SAME,
+ MERGE_OK = AV_MERGE_SAME,
+ AV_MERGE_DIFFERENT,
+};
+
void page_writeback_init(void);
static inline void *folio_raw_mapping(struct folio *folio)
diff --git a/mm/mmap.c b/mm/mmap.c
index ed91d0cd2111..10c76c6a3288 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1064,21 +1064,21 @@ static inline int is_mergeable_anon_vma(struct anon_vma *anon_vma1,
*/
if ((!anon_vma1 || !anon_vma2) && (!vma ||
list_is_singular(&vma->anon_vma_chain)))
- return 1;
+ return AV_MERGE_SAME;
if (anon_vma1 == anon_vma2)
- return 1;
+ return AV_MERGE_SAME;
/*
* Different anon_vma but not shared by several processes
*/
else if ((anon_vma1 && anon_vma2) &&
(anon_vma1 == anon_vma1->root)
&& (rbt_no_children(anon_vma1)))
- return 1;
+ return AV_MERGE_DIFFERENT;
/*
* Different anon_vma and shared -> unmergeable
*/
else
- return 0;
+ return AV_MERGE_FAILED;
}
/*
@@ -1099,12 +1099,10 @@ can_vma_merge_before(struct vm_area_struct *vma, unsigned long vm_flags,
struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
const char *anon_name)
{
- if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name) &&
- is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
+ if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name))
if (vma->vm_pgoff == vm_pgoff)
- return 1;
- }
- return 0;
+ return is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma);
+ return MERGE_FAILED;
}
/*
@@ -1121,14 +1119,13 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
const char *anon_name)
{
- if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name) &&
- is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma)) {
+ if (is_mergeable_vma(vma, file, vm_flags, vm_userfaultfd_ctx, anon_name)) {
pgoff_t vm_pglen;
vm_pglen = vma_pages(vma);
if (vma->vm_pgoff + vm_pglen == vm_pgoff)
- return 1;
+ return is_mergeable_anon_vma(anon_vma, vma->anon_vma, vma);
}
- return 0;
+ return MERGE_FAILED;
}
/*
@@ -1185,9 +1182,14 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
struct vm_area_struct *area, *next;
int err;
- int merge_prev = 0;
- int merge_both = 0;
- int merge_next = 0;
+ /*
+ * Following three variables are used to store values
+ * indicating wheather this VMA and its anon_vma can
+ * be merged and also the type of failure or success.
+ */
+ enum vma_merge_res merge_prev = MERGE_FAILED;
+ enum vma_merge_res merge_both = MERGE_FAILED;
+ enum vma_merge_res merge_next = MERGE_FAILED;
/*
* We later require that vma->vm_flags == vm_flags,
@@ -1210,38 +1212,39 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
* Can we merge predecessor?
*/
if (prev && prev->vm_end == addr &&
- mpol_equal(vma_policy(prev), policy) &&
- can_vma_merge_after(prev, vm_flags,
+ mpol_equal(vma_policy(prev), policy)) {
+ merge_prev = can_vma_merge_after(prev, vm_flags,
anon_vma, file, pgoff,
- vm_userfaultfd_ctx, anon_name)) {
- merge_prev = true;
+ vm_userfaultfd_ctx, anon_name);
}
+
/*
* Can we merge successor?
*/
if (next && end == next->vm_start &&
- mpol_equal(policy, vma_policy(next)) &&
- can_vma_merge_before(next, vm_flags,
+ mpol_equal(policy, vma_policy(next))) {
+ merge_next = can_vma_merge_before(next, vm_flags,
anon_vma, file, pgoff+pglen,
- vm_userfaultfd_ctx, anon_name)) {
- merge_next = true;
+ vm_userfaultfd_ctx, anon_name);
}
+
/*
* Can we merge both predecessor and successor?
*/
- if (merge_prev && merge_next)
+ if (merge_prev >= MERGE_OK && merge_next >= MERGE_OK) {
merge_both = is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL);
+ }
- if (merge_both) { /* cases 1, 6 */
+ if (merge_both >= MERGE_OK) { /* cases 1, 6 */
err = __vma_adjust(prev, prev->vm_start,
next->vm_end, prev->vm_pgoff, NULL,
prev);
area = prev;
- } else if (merge_prev) { /* cases 2, 5, 7 */
+ } else if (merge_prev >= MERGE_OK) { /* cases 2, 5, 7 */
err = __vma_adjust(prev, prev->vm_start,
end, prev->vm_pgoff, NULL, prev);
area = prev;
- } else if (merge_next) {
+ } else if (merge_next >= MERGE_OK) {
if (prev && addr < prev->vm_end) /* case 4 */
err = __vma_adjust(prev, prev->vm_start,
addr, prev->vm_pgoff, NULL, next);
@@ -1252,7 +1255,7 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
} else {
err = -1;
}
-
+ trace_vm_av_merge(err, merge_prev, merge_next, merge_both);
/*
* Cannot merge with predecessor or successor or error in __vma_adjust?
*/
@@ -3359,6 +3362,8 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
/*
* Source vma may have been merged into new_vma
*/
+ trace_vm_pgoff_merge(vma, anon_pgoff_updated);
+
if (unlikely(vma_start >= new_vma->vm_start &&
vma_start < new_vma->vm_end)) {
/*
--
2.34.1
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