Messages in this thread |  | | | Date | Wed, 27 May 2009 15:39:43 +0800 | | From | Huang Shijie <> | | Subject | Re: [PATCH] lib : provide a more precise radix_tree_gang_lookup_slot |
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>> diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h >> index 355f6e8..03e25f4 100644 >> --- a/include/linux/radix-tree.h >> +++ b/include/linux/radix-tree.h >> @@ -164,7 +164,8 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results, >> unsigned long first_index, unsigned int max_items); >> unsigned int >> radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results, >> - unsigned long first_index, unsigned int max_items); >> + unsigned long first_index, unsigned int max_items, >> + int contig); >> > > Variable `contig' could have the type `bool'. Did you consider and > reject that option, or just didn't think of it? > > > Yes, type `bool' is better. >> ... >> + if (contig) >> + goto out; >> + >> + } else if (contig) { >> + index--; >> + goto out; >> + >> + if (contig) { >> + if (slots_found == 0) >> + break; >> + if (next_index & RADIX_TREE_MAP_MASK) >> + break; >> + } >> - (void ***)pages, start, nr_pages); >> + (void ***)pages, start, nr_pages, 0); >> - (void ***)pages, index, nr_pages); >> + (void ***)pages, index, nr_pages, 1); >> > > The patch adds cycles in some cases and saves them in others. > > Does the saving exceed the adding? How do we know that the patch is a > net benefit? > >
Assume that: f0 = called frequency of find_get_pages() (contig == 0) f1 = called frequency of find_get_pages_contig() (contig == 1)
The primary user of find_get_pages() is ->writepage[s] of some file systems such as ext4. ( I think the shmem_lock() ,truncate() run occasionally which also call it.)
The primary user of find_get_pages_contig() is also the ->writepage[s] of some filesystem such as afs.( I am not sure whether btrfs is also the main user of it )
So if (f0 nearly equal f1) cycles saving >> cycles adding __lookup() saves much cycles when there are holes and the contig==1.
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