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pipe.7: Add a lot more detail on /proc files controlling memory usage by pipes 

Add a lot more detail on /proc/sys/fs/pipe-max-size and
/proc/sys/fs/pipe-user-pages-{soft,hard}.

Reviewed-by: Willy Tarreau <w@1wt.eu>
Reviewed-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2016-08-13 08:47:16 +12:00
parent 81c4577e23
commit 12033ac49d
1 changed files with 44 additions and 12 deletions
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man7/pipe.7
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@ -162,9 +162,19 @@ but is provided on many implementations.
.SS /proc files
On Linux, the following files control how much memory can be used for pipes:
.TP
.IR /proc/sys/fs/pipe-max-pages " (since Linux 2.6.34)"
.IR /proc/sys/fs/pipe-max-pages " (only in Linux 2.6.34)"
.\" commit b492e95be0ae672922f4734acf3f5d35c30be948
Deprecated since Linux 2.6.35.
An upper limit, in pages, on the capacity that an unprivileged user
(one without the
.BR CAP_SYS_RESOURCE
capability)
can set for a pipe.
The default value for this limit is 16 times the default pipe capacity
(see above); the lower limit is two pages.
This interface was removed in Linux 2.6.35, in favor of
.IR /proc/sys/fs/pipe-max-size .
.TP
.IR /proc/sys/fs/pipe-max-size " (since Linux 2.6.35)"
.\" commit ff9da691c0498ff81fdd014e7a0731dab2337dac
@ -172,24 +182,46 @@ The maximum size (in bytes) of individual pipes created or set by users
without the
.B CAP_SYS_RESOURCE
capability.
The default value for this file is 1048576.
Attempts to set a limit less than the page size cause
.BR write (2)
to fail with the error
.BR EINVAL .
.TP
.IR /proc/sys/fs/pipe-user-pages-hard " (since Linux 4.4)"
.IR /proc/sys/fs/pipe-user-pages-hard " (since Linux 4.5)"
.\" commit 759c01142a5d0f364a462346168a56de28a80f52
The combined maximum size (in pages) of all pipes created or set by a
single user without both the
The hard limit on the total size (in pages) of all pipes created or set by
a single unprivileged user (i.e., one with neither the
.B CAP_SYS_RESOURCE
and
nor the
.B CAP_SYS_ADMIN
capabilities.
capability).
So long as the total number of pages allocated to pipe buffers
for this user is at this limit,
attempts to create new pipes will be denied,
and attempts to increase a pipe's capacity will be denied.
When the value of this limit is zero (which is the default),
no hard limit is applied.
.\" The default was chosen to avoid breaking existing applications that
.\" make intensive use of pipes (e.g., for splicing).
.TP
.IR /proc/sys/fs/pipe-user-pages-soft " (since Linux 4.4)"
.IR /proc/sys/fs/pipe-user-pages-soft " (since Linux 4.5)"
.\" commit 759c01142a5d0f364a462346168a56de28a80f52
The combined size (in pages) of all pipes created or set by a single
user (without both the
The soft limit on the total size (in pages) of all pipes created or set by
a single unprivileged user (i.e., one with neither the
.B CAP_SYS_RESOURCE
and
nor the
.B CAP_SYS_ADMIN
capabilities) after which individual pipes will be limited to 1 page.
capability).
So long as the total number of pages allocated to pipe buffers
for this user is at this limit,
individual pipes created by a user will be limited to one page,
and attempts to increase a pipe's capacity will be denied.
When the value of this limit is zero, no soft limit is applied.
The default value for this file is 16384,
which permits creating up to 1024 pipes with the default capacity.
.\"
.SS PIPE_BUF
POSIX.1 says that