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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>
This commit is contained in:
Omar Sandoval 2018-08-21 21:55:13 -07:00 committed by Linus Torvalds
parent 37e949bd52
commit bf991c2231
1 changed files with 11 additions and 3 deletions
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14
fs/proc/kcore.c
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@ -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) {