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[PATCH] cpuset: update cpuset_zones_allowed comment

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Update the kernel/cpuset.c:cpuset_zone_allowed() comment.

The rule for when mm/page_alloc.c should call cpuset_zone_allowed()
was intended to be:

  Don't call cpuset_zone_allowed() if you can't sleep, unless you
  pass in the __GFP_HARDWALL flag set in gfp_flag, which disables
  the code that might scan up ancestor cpusets and sleep.

The explanation of this rule in the comment above cpuset_zone_allowed() was
stale, as a result of a restructuring of some __alloc_pages() code in
November 2005.

Rewrite that comment ...

Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Paul Jackson 2006-05-20 15:00:10 -07:00 committed by Linus Torvalds
parent bdd804f478
commit 36be57ffe3
1 changed files with 14 additions and 8 deletions
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22
kernel/cpuset.c
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@ -2231,19 +2231,25 @@ static const struct cpuset *nearest_exclusive_ancestor(const struct cpuset *cs)
* So only GFP_KERNEL allocations, if all nodes in the cpuset are
* short of memory, might require taking the callback_mutex mutex.
*
* The first loop over the zonelist in mm/page_alloc.c:__alloc_pages()
* calls here with __GFP_HARDWALL always set in gfp_mask, enforcing
* hardwall cpusets - no allocation on a node outside the cpuset is
* allowed (unless in interrupt, of course).
* The first call here from mm/page_alloc:get_page_from_freelist()
* has __GFP_HARDWALL set in gfp_mask, enforcing hardwall cpusets, so
* no allocation on a node outside the cpuset is allowed (unless in
* interrupt, of course).
*
* The second loop doesn't even call here for GFP_ATOMIC requests
* (if the __alloc_pages() local variable 'wait' is set). That check
* and the checks below have the combined affect in the second loop of
* the __alloc_pages() routine that:
* The second pass through get_page_from_freelist() doesn't even call
* here for GFP_ATOMIC calls. For those calls, the __alloc_pages()
* variable 'wait' is not set, and the bit ALLOC_CPUSET is not set
* in alloc_flags. That logic and the checks below have the combined
* affect that:
* in_interrupt - any node ok (current task context irrelevant)
* GFP_ATOMIC - any node ok
* GFP_KERNEL - any node in enclosing mem_exclusive cpuset ok
* GFP_USER - only nodes in current tasks mems allowed ok.
*
* Rule:
* Don't call cpuset_zone_allowed() if you can't sleep, unless you
* pass in the __GFP_HARDWALL flag set in gfp_flag, which disables
* the code that might scan up ancestor cpusets and sleep.
**/
int __cpuset_zone_allowed(struct zone *z, gfp_t gfp_mask)