netdev - Re: [PATCH 03/31] mm: expose gfp_to_alloc

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Date:	Fri, 2 Oct 2009 15:04:10 +1000
From:	Neil Brown <neilb@...e.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Suresh Jayaraman <sjayaraman@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	netdev@...r.kernel.org, Miklos Szeredi <mszeredi@...e.cz>,
	Wouter Verhelst <w@...r.be>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	trond.myklebust@....uio.no
Subject: Re: [PATCH 03/31] mm: expose gfp_to_alloc_flags()

On Thursday October 1, rientjes@...gle.com wrote:
> On Thu, 1 Oct 2009, Suresh Jayaraman wrote:
> 
> > From: Peter Zijlstra <a.p.zijlstra@...llo.nl> 
> > 
> > Expose the gfp to alloc_flags mapping, so we can use it in other parts
> > of the vm.
> > 
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Signed-off-by: Suresh Jayaraman <sjayaraman@...e.de>
> 
> Nack, these flags are internal to the page allocator and exporting them to 
> generic VM code is unnecessary.
> 
> The only bit you actually use in your patchset is ALLOC_NO_WATERMARKS to 
> determine whether a particular allocation can use memory reserves.  I'd 
> suggest adding a bool function that returns whether the current context is 
> given access to reserves including your new __GFP_MEMALLOC flag and 
> exporting that instead.

That sounds like a very appropriate suggestion, thanks.

So something like this?
Then change every occurrence of
+		if (!(gfp_to_alloc_flags(gfpflags) & ALLOC_NO_WATERMARKS))
to
+		if (!(gfp_has_no_watermarks(gfpflags)))

??

Thanks,
NeilBrown



diff --git a/mm/internal.h b/mm/internal.h
index 22ec8d2..7ff78d6 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -195,6 +195,8 @@ static inline struct page *mem_map_next(struct page *iter,
 #define __paginginit __init
 #endif
 
+int gfp_has_no_watermarks(gfp_t gfp_mask);
+
 /* Memory initialisation debug and verification */
 enum mminit_level {
 	MMINIT_WARNING,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bf72055..4b4292a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1782,6 +1782,11 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
 	return alloc_flags;
 }
 
+int gfp_has_no_watermarks(gfp_t gfp_mask)
+{
+	return (gfp_to_alloc_flags(gfp_mask) & ALLOC_NO_WATERMARKS);
+}
+
 static inline struct page *
 __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	struct zonelist *zonelist, enum zone_type high_zoneidx,
--
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