The patch titled
Subject: mm: pagemap: restrict pagewalk to the requested range
has been added to the -mm mm-unstable branch. Its filename is
mm-pagemap-restrict-pagewalk-to-the-requested-range.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-pagemap-restrict-pagewalk-to-the-requested-range.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Yuanchu Xie <yuanchu@xxxxxxxxxx>
Subject: mm: pagemap: restrict pagewalk to the requested range
Date: Tue, 16 May 2023 01:26:08 +0800
The pagewalk in pagemap_read reads one PTE past the end of the requested
range, and stops when the buffer runs out of space. While it produces
the right result, the extra read is unnecessary and less performant.
I timed the following command before and after this patch:
dd count=100000 if=/proc/self/pagemap of=/dev/null
The results are consistently within 0.001s across 5 runs.
Before:
100000+0 records in
100000+0 records out
51200000 bytes (51 MB) copied, 0.0763159 s, 671 MB/s
real 0m0.078s
user 0m0.012s
sys 0m0.065s
After:
100000+0 records in
100000+0 records out
51200000 bytes (51 MB) copied, 0.0487928 s, 1.0 GB/s
real 0m0.050s
user 0m0.011s
sys 0m0.039s
Link: https://lkml.kernel.org/r/20230515172608.3558391-1-yuanchu@xxxxxxxxxx
Signed-off-by: Yuanchu Xie <yuanchu@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Zach O'Keefe <zokeefe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/task_mmu.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
--- a/fs/proc/task_mmu.c~mm-pagemap-restrict-pagewalk-to-the-requested-range
+++ a/fs/proc/task_mmu.c
@@ -1689,23 +1689,23 @@ static ssize_t pagemap_read(struct file
/* watch out for wraparound */
start_vaddr = end_vaddr;
if (svpfn <= (ULONG_MAX >> PAGE_SHIFT)) {
+ unsigned long end;
+
ret = mmap_read_lock_killable(mm);
if (ret)
goto out_free;
start_vaddr = untagged_addr_remote(mm, svpfn << PAGE_SHIFT);
mmap_read_unlock(mm);
+
+ end = start_vaddr + ((count / PM_ENTRY_BYTES) << PAGE_SHIFT);
+ if (end >= start_vaddr && end < mm->task_size)
+ end_vaddr = end;
}
/* Ensure the address is inside the task */
if (start_vaddr > mm->task_size)
start_vaddr = end_vaddr;
- /*
- * The odds are that this will stop walking way
- * before end_vaddr, because the length of the
- * user buffer is tracked in "pm", and the walk
- * will stop when we hit the end of the buffer.
- */
ret = 0;
while (count && (start_vaddr < end_vaddr)) {
int len;
_
Patches currently in -mm which might be from yuanchu@xxxxxxxxxx are
mm-pagemap-restrict-pagewalk-to-the-requested-range.patch
