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authorNick Piggin <npiggin@suse.de>2008-07-25 19:45:22 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-07-26 12:00:05 -0700
commit21cc199baa815d7b3f1ace4be20b9558cbddc00f (patch)
treeeb4f3fa42a83613e2fe586b2555a811740952dce
parenta0a8f5364a5ad248aec6cb705e0092ff563edc2f (diff)
downloadop-kernel-dev-21cc199baa815d7b3f1ace4be20b9558cbddc00f.zip
op-kernel-dev-21cc199baa815d7b3f1ace4be20b9558cbddc00f.tar.gz
mm: introduce get_user_pages_fast
Introduce a new get_user_pages_fast mm API, which is basically a get_user_pages with a less general API (but still tends to be suited to the common case): - task and mm are always current and current->mm - force is always 0 - pages is always non-NULL - don't pass back vmas This restricted API can be implemented in a much more scalable way on many architectures when the ptes are present, by walking the page tables locklessly (no mmap_sem or page table locks). When the ptes are not populated, get_user_pages_fast() could be slower. This is implemented locklessly on x86, and used in some key direct IO call sites, in later patches, which provides nearly 10% performance improvement on a threaded database workload. Lots of other code could use this too, depending on use cases (eg. grep drivers/). And it might inspire some new and clever ways to use it. [akpm@linux-foundation.org: build fix] [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Dave Kleikamp <shaggy@austin.ibm.com> Cc: Andy Whitcroft <apw@shadowen.org> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Andi Kleen <andi@firstfloor.org> Cc: Dave Kleikamp <shaggy@austin.ibm.com> Cc: Badari Pulavarty <pbadari@us.ibm.com> Cc: Zach Brown <zach.brown@oracle.com> Cc: Jens Axboe <jens.axboe@oracle.com> Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/mm.h33
1 files changed, 33 insertions, 0 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index d87a5a5..f3fd70d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -833,6 +833,39 @@ extern int mprotect_fixup(struct vm_area_struct *vma,
struct vm_area_struct **pprev, unsigned long start,
unsigned long end, unsigned long newflags);
+#ifdef CONFIG_HAVE_GET_USER_PAGES_FAST
+/*
+ * get_user_pages_fast provides equivalent functionality to get_user_pages,
+ * operating on current and current->mm (force=0 and doesn't return any vmas).
+ *
+ * get_user_pages_fast may take mmap_sem and page tables, so no assumptions
+ * can be made about locking. get_user_pages_fast is to be implemented in a
+ * way that is advantageous (vs get_user_pages()) when the user memory area is
+ * already faulted in and present in ptes. However if the pages have to be
+ * faulted in, it may turn out to be slightly slower).
+ */
+int get_user_pages_fast(unsigned long start, int nr_pages, int write,
+ struct page **pages);
+
+#else
+/*
+ * Should probably be moved to asm-generic, and architectures can include it if
+ * they don't implement their own get_user_pages_fast.
+ */
+#define get_user_pages_fast(start, nr_pages, write, pages) \
+({ \
+ struct mm_struct *mm = current->mm; \
+ int ret; \
+ \
+ down_read(&mm->mmap_sem); \
+ ret = get_user_pages(current, mm, start, nr_pages, \
+ write, 0, pages, NULL); \
+ up_read(&mm->mmap_sem); \
+ \
+ ret; \
+})
+#endif
+
/*
* A callback you can register to apply pressure to ageable caches.
*
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