From: Omar Sandoval <osandov@xxxxxx> Subject: 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@xxxxxx Signed-off-by: Omar Sandoval <osandov@xxxxxx> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> Cc: Bhupesh Sharma <bhsharma@xxxxxxxxxx> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx> Cc: James Morse <james.morse@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/proc/kcore.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) --- a/fs/proc/kcore.c~proc-kcore-optimize-multiple-page-reads +++ a/fs/proc/kcore.c @@ -428,10 +428,18 @@ read_kcore(struct file *file, char __use 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) { _
