Re: [PATCHv2, RFC 07/30] thp, mm: introduce mapping_can_have_hugepages() predicate

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On 04/05/2013 11:45 AM, Ric Mason wrote:
Hi Kirill,
On 03/15/2013 01:50 AM, Kirill A. Shutemov wrote:
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>

Returns true if mapping can have huge pages. Just check for __GFP_COMP
in gfp mask of the mapping for now.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
  include/linux/pagemap.h |   10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index e3dea75..3521b0d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -84,6 +84,16 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
                  (__force unsigned long)mask;
  }
+static inline bool mapping_can_have_hugepages(struct address_space *m)
+{
+    if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
+        gfp_t gfp_mask = mapping_gfp_mask(m);
+        return !!(gfp_mask & __GFP_COMP);

I always see !! in kernel, but why check directly instead of have !! prefix?

s/why/why not


+    }
+
+    return false;
+}
+
  /*
   * The page cache can done in larger chunks than
   * one page, because it allows for more efficient


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