[lkml]   [2017]   [Jul]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH RFC] tty: don't force !TTYB_NORMAL flip buffers if not required
In change acc0f67f30, we introduced flip buffers that skipped allocation
of the flags buffer for characters received with TTY_NORMAL flags.

However, the slow path of tty_insert_flip_char() calls
tty_insert_flip_string_flags() (providing a flag buffer pointer), which
forces the buffer code to allocate a !TTYB_NORMAL buffer. If we took the
slow path due to running out of buffer space, rather than seeing
!TTY_NORMAL flags, we've needlessly allocated a flags buffer.

This change uses tty_insert_flip_string_fixed_flag instead, which will
allocate TTYB_NORMAL buffers if flag == TTY_NORMAL. Since we're only
inserting one character, it's fine for the flag to be "fixed".

Signed-off-by: Jeremy Kerr <>
CC: Peter Hurley <>

RFC: I'm certainly no expert on the tty layer, and perhaps there's a
good reason to always allocate a flags buffer. However, this seems to
relieve buffer pressure in my tests.

include/linux/tty_flip.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/tty_flip.h b/include/linux/tty_flip.h
index c28dd52..15d03a1 100644
--- a/include/linux/tty_flip.h
+++ b/include/linux/tty_flip.h
@@ -26,7 +26,7 @@ static inline int tty_insert_flip_char(struct tty_port *port,
*char_buf_ptr(tb, tb->used++) = ch;
return 1;
- return tty_insert_flip_string_flags(port, &ch, &flag, 1);
+ return tty_insert_flip_string_fixed_flag(port, &ch, flag, 1);

static inline int tty_insert_flip_string(struct tty_port *port,
 \ /
  Last update: 2017-07-25 10:58    [W:0.018 / U:10.100 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site