* PID_MAX_LIMIT limit on ia32?
@ 2010-11-24 20:22 Davy Durham
0 siblings, 0 replies; only message in thread
From: Davy Durham @ 2010-11-24 20:22 UTC (permalink / raw)
To: linux-kernel
I have searched around without a definitive answer to my question.
PID_MAX_LIMIT is currently defined as:
/*
* A maximum of 4 million PIDs should be enough for a while.
* [NOTE: PID/TIDs are limited to 2^29 ~= 500+ million, see
futex.h.]
*/
#define PID_MAX_LIMIT (CONFIG_BASE_SMALL ? PAGE_SIZE * 8 :
(sizeof(long) > 4 ? 4 * 1024 * 1024 : PID_MAX_DEFAULT))
And PID_MAX_DEFAULT is normally 32k.
I found a comment on the net:
“When recycling PID numbers, the kernel must manage a
pidmap_array bitmap that denotes which are the PIDs currently
assigned and which are the free ones. Because a page frame
contains 32,768 bits, in 32-bit architectures the pidmap_array
bitmap is stored in a single page. In 64-bit architectures,
however, additional pages can be added to the bitmap when the
kernel assigns a PID number too large for the current bitmap
size. These pages are never released.”
Which may seem to indicate that PID_MAX_DEFAULT cannot be more than 1
memory page on 32bit archs.
Can the PID_MAX_LIMIT #define be increased safely on the ia32 arch which
would cause pidmap_array to use more than one memory page? (say 4 pages
or so).
I thought about just compiling it and testing things, but was unsure if
I would run into problems long-term.
[Please CC me on the response as I'm not currently subscribed]
TIA,
Davy
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