From bf991c2231117d50a7645792b514354fc8d19dae Mon Sep 17 00:00:00 2001
From: Omar Sandoval <osandov@fb.com>
Date: Tue, 21 Aug 2018 21:55:13 -0700
Subject: [PATCH] proc/kcore: optimize multiple page reads
The current code does a full search of the segment list every time for
every page. This is wasteful, since it's almost certain that the next
page will be in the same segment. Instead, check if the previous segment
covers the current page before doing the list search.
Link: http://lkml.kernel.org/r/fd346c11090cf93d867e01b8d73a6567c5ac6361.1531953780.git.osandov@fb.com
Signed-off-by: Omar Sandoval <osandov@fb.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Bhupesh Sharma <bhsharma@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: James Morse <james.morse@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
fs/proc/kcore.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 808ef9afd0840..758c14e46a44e 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -428,10 +428,18 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
tsz = buflen;
+ m = NULL;
while (buflen) {
- list_for_each_entry(m, &kclist_head, list) {
- if (start >= m->addr && start < (m->addr+m->size))
- break;
+ /*
+ * If this is the first iteration or the address is not within
+ * the previous entry, search for a matching entry.
+ */
+ if (!m || start < m->addr || start >= m->addr + m->size) {
+ list_for_each_entry(m, &kclist_head, list) {
+ if (start >= m->addr &&
+ start < m->addr + m->size)
+ break;
+ }
}
if (&m->list == &kclist_head) {
--
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