linux-kernel - [061/116] tty: Keep the default buffering to sub-page units

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20100330225638.054650490@linux.site>
Date:	Tue, 30 Mar 2010 15:55:39 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Alan Cox <alan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [061/116] tty: Keep the default buffering to sub-page units

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Alan Cox <alan@...ux.intel.com>

commit d9661adfb8e53a7647360140af3b92284cbe52d4 upstream.

We allocate during interrupts so while our buffering is normally diced up
small anyway on some hardware at speed we can pressure the VM excessively
for page pairs. We don't really need big buffers to be linear so don't try
so hard.

In order to make this work well we will tidy up excess callers to request_room,
which cannot itself enforce this break up.

Signed-off-by: Alan Cox <alan@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/char/tty_buffer.c |    6 ++++--
 include/linux/tty.h       |   10 ++++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

--- a/drivers/char/tty_buffer.c
+++ b/drivers/char/tty_buffer.c
@@ -247,7 +247,8 @@ int tty_insert_flip_string(struct tty_st
 {
 	int copied = 0;
 	do {
-		int space = tty_buffer_request_room(tty, size - copied);
+		int goal = min(size - copied, TTY_BUFFER_PAGE);
+		int space = tty_buffer_request_room(tty, goal);
 		struct tty_buffer *tb = tty->buf.tail;
 		/* If there is no space then tb may be NULL */
 		if (unlikely(space == 0))
@@ -283,7 +284,8 @@ int tty_insert_flip_string_flags(struct
 {
 	int copied = 0;
 	do {
-		int space = tty_buffer_request_room(tty, size - copied);
+		int goal = min(size - copied, TTY_BUFFER_PAGE);
+		int space = tty_buffer_request_room(tty, goal);
 		struct tty_buffer *tb = tty->buf.tail;
 		/* If there is no space then tb may be NULL */
 		if (unlikely(space == 0))
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -68,6 +68,16 @@ struct tty_buffer {
 	unsigned long data[0];
 };
 
+/*
+ * We default to dicing tty buffer allocations to this many characters
+ * in order to avoid multiple page allocations. We assume tty_buffer itself
+ * is under 256 bytes. See tty_buffer_find for the allocation logic this
+ * must match
+ */
+
+#define TTY_BUFFER_PAGE		((PAGE_SIZE  - 256) / 2)
+
+
 struct tty_bufhead {
 	struct delayed_work work;
 	spinlock_t lock;


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/