On 08/14/2016 01:13 AM, Michael Kerrisk (man-pages) wrote:
Thanks. I've added this text to pipe(7) (rather than pipe(2)), and
expanded it considerably:
Good idea!
/proc files
On Linux, the following files control how much memory can be used
for pipes:
/proc/sys/fs/pipe-max-pages (only in Linux 2.6.34)
An upper limit, in pages, on the capacity that an unprivi‐
leged user (one without the 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 /proc/sys/fs/pipe-max-size.
/proc/sys/fs/pipe-max-size (since Linux 2.6.35)
The maximum size (in bytes) of individual pipes created or
I think I had a mistake in my original text because this limit is not
checked at creation time (the default pipe size, PIPE_DEF_BUFFERS, is
used even when it is greater than pipe-max-size), so maybe we can take
out the "created or".
set by users without the CAP_SYS_RESOURCE capability. The
default value for this file is 1048576. Attempts to set a
limit less than the page size cause write(2) to fail with
the error EINVAL.
Maybe add in a paranthesis that 1048576 is 1 MiB?
/proc/sys/fs/pipe-user-pages-hard (since Linux 4.5)
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 CAP_SYS_RESOURCE nor the CAP_SYS_ADMIN
capability). So long as the total number of pages allo‐
cated 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.
/proc/sys/fs/pipe-user-pages-soft (since Linux 4.5)
The soft limit on the total size (in pages) of all pipes
created or set by a single unprivileged user (.e., one with
neither the CAP_SYS_RESOURCE nor the CAP_SYS_ADMIN capabil‐
ity). 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 capac‐
ity.
How does the above seem?
It looks great, thanks for cleaning up my measly attempt.
Vegard
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