[PATCH] Remove references to sbrk to grow/shrink arenas

[PATCH] Remove references to sbrk to grow/shrink arenas

[Siddhesh Poyarekar]

The manual incorrectly references sbrk as the method used to grow and
shrink heaps and the fact that M_TRIM_THRESHOLD and M_TOP_PAD control
that behavior.  In reality, a heap may be grown or shrunk through
multiple methods depending on whether it is the main arena (in which
case sbrk is correct) or not (in which case, there are a number of
strategies including allocating an additional heap to grow an arena
and/or 'mprotect' a region to make it available for allocation).

Remove references to sbrk so that it covers the behavior more
accurately.

	* manual/memory.texi (M_TOP_PAD): Remove reference to sbrk.
	(M_TRIM_THRESHOLD): Likewise.
---
 manual/memory.texi | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/manual/memory.texi b/manual/memory.texi
index b98dcf2..8ef2bbd 100644
--- a/manual/memory.texi
+++ b/manual/memory.texi
@@ -1138,18 +1138,16 @@ overwritten.
 This parameter can also be set for the process at startup by setting the
 environment variable @code{MALLOC_MMAP_PERTURB_} to the desired value.
 @item M_TOP_PAD
-This parameter determines the amount of extra memory to obtain from the
-system when a call to @code{sbrk} is required.  It also specifies the
-number of bytes to retain when shrinking the heap by calling @code{sbrk}
-with a negative argument.  This provides the necessary hysteresis in
-heap size such that excessive amounts of system calls can be avoided.
+This parameter determines the amount of extra memory to obtain from the system
+when an arena needs to be extended.  It also specifies the number of bytes to
+retain when shrinking an arena.  This provides the necessary hysteresis in heap
+size such that excessive amounts of system calls can be avoided.
 
 This parameter can also be set for the process at startup by setting the
 environment variable @code{MALLOC_TOP_PAD_} to the desired value.
 @item M_TRIM_THRESHOLD
 This is the minimum size (in bytes) of the top-most, releasable chunk
-that will cause @code{sbrk} to be called with a negative argument in
-order to return memory to the system.
+that will trigger a system call in order to return memory to the system.
 
 This parameter can also be set for the process at startup by setting the
 environment variable @code{MALLOC_TRIM_THRESHOLD_} to the desired value.
-- 
2.7.4

Re: [PATCH] Remove references to sbrk to grow/shrink arenas

[DJ Delorie]

Siddhesh Poyarekar <siddhesh@sourceware.org> writes:
> 	* manual/memory.texi (M_TOP_PAD): Remove reference to sbrk.
> 	(M_TRIM_THRESHOLD): Likewise.

These changes look good to me from the malloc side of things.

Re: [PATCH] Remove references to sbrk to grow/shrink arenas

[Siddhesh Poyarekar]

On Monday 10 October 2016 11:10 PM, DJ Delorie wrote:
> 
> Siddhesh Poyarekar <siddhesh@sourceware.org> writes:
>> 	* manual/memory.texi (M_TOP_PAD): Remove reference to sbrk.
>> 	(M_TRIM_THRESHOLD): Likewise.
> 
> These changes look good to me from the malloc side of things.
> 

Thanks, pushed.

Siddhesh