From: Omar Sandoval <osandov@osandov.com>
To: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>,
Eric Biederman <ebiederm@xmission.com>,
James Morse <james.morse@arm.com>,
Bhupesh Sharma <bhsharma@redhat.com>,
kernel-team@fb.com
Subject: [PATCH v4 7/9] proc/kcore: optimize multiple page reads
Date: Wed, 25 Jul 2018 16:59:18 -0700 [thread overview]
Message-ID: <c9e919ab66d4064451bb7b613bfead17d8986c88.1532563124.git.osandov@fb.com> (raw)
In-Reply-To: <cover.1532563124.git.osandov@fb.com>
From: Omar Sandoval <osandov@fb.com>
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.
Signed-off-by: Omar Sandoval <osandov@fb.com>
---
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 808ef9afd084..758c14e46a44 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) {
--
2.18.0
next prev parent reply other threads:[~2018-07-25 23:59 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-25 23:59 [PATCH v4 0/9] /proc/kcore improvements Omar Sandoval
2018-07-25 23:59 ` [PATCH v4 1/9] proc/kcore: don't grab lock for kclist_add() Omar Sandoval
2018-08-07 5:05 ` Bhupesh Sharma
2018-07-25 23:59 ` [PATCH v4 2/9] proc/kcore: don't grab lock for memory hotplug notifier Omar Sandoval
2018-07-25 23:59 ` [PATCH v4 3/9] proc/kcore: replace kclist_lock rwlock with rwsem Omar Sandoval
2018-07-25 23:59 ` [PATCH v4 4/9] proc/kcore: fix memory hotplug vs multiple opens race Omar Sandoval
2018-07-25 23:59 ` [PATCH v4 5/9] proc/kcore: hold lock during read Omar Sandoval
2018-07-25 23:59 ` [PATCH v4 6/9] proc/kcore: clean up ELF header generation Omar Sandoval
2018-07-25 23:59 ` Omar Sandoval [this message]
2018-07-25 23:59 ` [PATCH v4 8/9] crash_core: use VMCOREINFO_SYMBOL_ARRAY() for swapper_pg_dir Omar Sandoval
2018-07-25 23:59 ` [PATCH v4 9/9] proc/kcore: add vmcoreinfo note to /proc/kcore Omar Sandoval
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