Messages in this thread | | | Subject | Re: [PATCH 02/13] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages | From | Mel Gorman <> | Date | Tue, 26 Apr 2011 12:33:48 +0100 |
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On Tue, 2011-04-26 at 21:15 +1000, NeilBrown wrote: > On Tue, 26 Apr 2011 08:36:43 +0100 Mel Gorman <mgorman@suse.de> wrote: > > > +bool gfp_pfmemalloc_allowed(gfp_t gfp_mask) > > +{ > > + return gfp_to_alloc_flags(gfp_mask) & ALLOC_PFMEMALLOC; > > +} > > + > > static inline struct page * > > __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > > struct zonelist *zonelist, enum zone_type high_zoneidx, > > @@ -2202,8 +2211,16 @@ nopage: > > got_pg: > > if (kmemcheck_enabled) > > kmemcheck_pagealloc_alloc(page, order, gfp_mask); > > - return page; > > > > + /* > > + * page->pfmemalloc is set when the caller had PFMEMALLOC set or is > > + * been OOM killed. The expectation is that the caller is taking > > + * steps that will free more memory. The caller should avoid the > > + * page being used for !PFMEMALLOC purposes. > > + */ > > + page->pfmemalloc = (alloc_flags & ALLOC_PFMEMALLOC); > > + > > + return page; > > Linus doesn't seem to be a fan of this construct: > https://lkml.org/lkml/2011/4/1/255 >
There is confusion around this topic. Andrew prefers bool for true/false values and it's self-documenting. I tend to prefer it myself for readability and there is a slow conversion in the VM from ints-used-as-bools to bools and my understanding of bool is that any non-zero value will be treated as true (just as it is for int).
> pfmemalloc is a bool, and the value on the right is either 0 or 0x1000. > > If bool happens to be typedefed to 'char' or even 'short', pfmemalloc would > always be set to 0.
It is typedeffed as _Bool though which I thought was able to handle the cast appropriately or is that wrong?
> Ditto for the gfp_pfmemalloc_allowed function. > > Prefixing with '!!' would make it safe. >
Will do that to avoid any oddities. Thanks
-- Mel Gorman SUSE Labs
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