Hello Vegard, On 08/14/2016 07:41 PM, Vegard Nossum wrote: > 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". Hmmm -- that's true. It seems a little weird that one can create a pipe whose initial size exceeds pipe-max-size. Should we fix that in the kernel? (I can add a third patch to my series.) Setting pipe-max-size lower than PIPE_DEF_BUFFERS is an admittedly an odd set up, so maybe it's not worth changing the code(?). I removed 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? Done. >> >> /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. No problem. Yet again, documenting the API well finds some interesting bugs ;-). Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
