diff options
author | Davide Libenzi <davidel@xmailserver.org> | 2008-12-01 13:13:55 -0800 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@suse.de> | 2008-12-05 10:55:12 -0800 |
commit | 284483e971f807ad4e4d71a2e65458afa8b7fb1f (patch) | |
tree | 4e8bfd9739bdd0477324854af0796cdcc7cf8e5f /Documentation | |
parent | 16a476e1419249a1c0733fdb683f29c9bde6f941 (diff) | |
download | linux-stable-284483e971f807ad4e4d71a2e65458afa8b7fb1f.tar.gz linux-stable-284483e971f807ad4e4d71a2e65458afa8b7fb1f.tar.bz2 linux-stable-284483e971f807ad4e4d71a2e65458afa8b7fb1f.zip |
epoll: introduce resource usage limits
commit 7ef9964e6d1b911b78709f144000aacadd0ebc21 upstream.
It has been thought that the per-user file descriptors limit would also
limit the resources that a normal user can request via the epoll
interface. Vegard Nossum reported a very simple program (a modified
version attached) that can make a normal user to request a pretty large
amount of kernel memory, well within the its maximum number of fds. To
solve such problem, default limits are now imposed, and /proc based
configuration has been introduced. A new directory has been created,
named /proc/sys/fs/epoll/ and inside there, there are two configuration
points:
max_user_instances = Maximum number of devices - per user
max_user_watches = Maximum number of "watched" fds - per user
The current default for "max_user_watches" limits the memory used by epoll
to store "watches", to 1/32 of the amount of the low RAM. As example, a
256MB 32bit machine, will have "max_user_watches" set to roughly 90000.
That should be enough to not break existing heavy epoll users. The
default value for "max_user_instances" is set to 128, that should be
enough too.
This also changes the userspace, because a new error code can now come out
from EPOLL_CTL_ADD (-ENOSPC). The EMFILE from epoll_create() was already
listed, so that should be ok.
[akpm@linux-foundation.org: use get_current_user()]
Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Reported-by: Vegard Nossum <vegardno@ifi.uio.no>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/filesystems/proc.txt | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index f566ad9bcb7b..23f3edc0bde0 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -44,6 +44,7 @@ Table of Contents 2.14 /proc/<pid>/io - Display the IO accounting fields 2.15 /proc/<pid>/coredump_filter - Core dump filtering settings 2.16 /proc/<pid>/mountinfo - Information about mounts + 2.17 /proc/sys/fs/epoll - Configuration options for the epoll interface ------------------------------------------------------------------------------ Preface @@ -2471,4 +2472,30 @@ For more information on mount propagation see: Documentation/filesystems/sharedsubtree.txt +2.17 /proc/sys/fs/epoll - Configuration options for the epoll interface +-------------------------------------------------------- + +This directory contains configuration options for the epoll(7) interface. + +max_user_instances +------------------ + +This is the maximum number of epoll file descriptors that a single user can +have open at a given time. The default value is 128, and should be enough +for normal users. + +max_user_watches +---------------- + +Every epoll file descriptor can store a number of files to be monitored +for event readiness. Each one of these monitored files constitutes a "watch". +This configuration option sets the maximum number of "watches" that are +allowed for each user. +Each "watch" costs roughly 90 bytes on a 32bit kernel, and roughly 160 bytes +on a 64bit one. +The current default value for max_user_watches is the 1/32 of the available +low memory, divided for the "watch" cost in bytes. + + ------------------------------------------------------------------------------ + |