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authorDavide Libenzi <davidel@xmailserver.org>2008-12-01 13:13:55 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2008-12-01 19:55:24 -0800
commit7ef9964e6d1b911b78709f144000aacadd0ebc21 (patch)
tree30667d0a2f8e53973ff48d2c02df48bbc6fe74aa /Documentation
parentb7d271df873c5121a4ca1c70dea126b5920ec2f1 (diff)
downloadop-kernel-dev-7ef9964e6d1b911b78709f144000aacadd0ebc21.zip
op-kernel-dev-7ef9964e6d1b911b78709f144000aacadd0ebc21.tar.gz
epoll: introduce resource usage limits
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: <stable@kernel.org> 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>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/proc.txt27
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index bcceb99..bb1b0dd 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
@@ -2483,4 +2484,30 @@ 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.
+
+
------------------------------------------------------------------------------
+
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