[patch] mm: document tree_lock->zone.lock lockorder

[patch] mm: document tree_lock->zone.lock lockorder

[Nick Piggin]

If you won't take the patch to move allocation out from under tree_lock,
please apply this update to lock ordering comments.

zone->lock is quite an "inner" lock and mostly constrained to page alloc
as well, so like slab locks, it probably isn't something that is critically
important to document here. However unlike slab locks, zone lock could be
used more widely in future, and page_alloc.c might possibly have more
business to do tricky things with pagecache than does slab. So... I don't
think it hurts to document it.

Signed-off-by: Nick Piggin <npiggin@suse.de>
---
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -63,6 +63,7 @@ generic_file_direct_IO(int rw, struct ki
  *    ->private_lock		(__free_pte->__set_page_dirty_buffers)
  *      ->swap_lock		(exclusive_swap_page, others)
  *        ->mapping->tree_lock
+ *          ->zone.lock
  *
  *  ->i_mutex
  *    ->i_mmap_lock		(truncate->unmap_mapping_range)
Index: linux-2.6/mm/rmap.c
===================================================================
--- linux-2.6.orig/mm/rmap.c
+++ linux-2.6/mm/rmap.c
@@ -36,6 +36,7 @@
  *                 mapping->tree_lock (widely used, in set_page_dirty,
  *                           in arch-dependent flush_dcache_mmap_lock,
  *                           within inode_lock in __sync_single_inode)
+ *                   zone->lock (within radix tree node alloc)
  */
 
 #include <linux/mm.h>

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Re: [patch] mm: document tree_lock->zone.lock lockorder

[Andrew Morton]

On Fri, 28 Sep 2007 17:55:36 +0200
Nick Piggin <npiggin@suse.de> wrote:

> If you won't take the patch to move allocation out from under tree_lock,

rofl@nick.  My memory of patches only extends back for the previous
10000 or so.  You'll need to put a tad more effort into telling us
what you're referring to, sorry.

> please apply this update to lock ordering comments.

no probs, thanks.

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Re: [patch] mm: document tree_lock->zone.lock lockorder

[Nick Piggin]

On Fri, Sep 28, 2007 at 04:20:39PM -0700, Andrew Morton wrote:
> On Fri, 28 Sep 2007 17:55:36 +0200
> Nick Piggin <npiggin@suse.de> wrote:
> 
> > If you won't take the patch to move allocation out from under tree_lock,
> 
> rofl@nick.  My memory of patches only extends back for the previous
> 10000 or so.  You'll need to put a tad more effort into telling us
> what you're referring to, sorry.

Just the patch to default the radix tree node allocation to use the
preload (which will be guaranteed to be full) before falling back to
doing atomic allocations under the tree_lock.

At the moment, it defaults to doing these atomic allocations first,
and leaves the preload alone, even though we've just done all the work
to allocate it under GFP_KERNEL.

Anyway.


> > please apply this update to lock ordering comments.
> 
> no probs, thanks.

Thanks.

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