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authorHugh Dickins <hughd@google.com>2011-08-03 16:21:19 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-08-03 14:25:22 -1000
commita2c16d6cb0e478812829ca84aeabd02e36af35eb (patch)
tree7803a522da5deee7ce753dc5404dca01f42aa176 /include/linux/swapops.h
parent6328650bb4d854a7dc1498d1c0048b838b0d340c (diff)
mm: let swap use exceptional entries
If swap entries are to be stored along with struct page pointers in a radix tree, they need to be distinguished as exceptional entries. Most of the handling of swap entries in radix tree will be contained in shmem.c, but a few functions in filemap.c's common code need to check for their appearance: find_get_page(), find_lock_page(), find_get_pages() and find_get_pages_contig(). So as not to slow their fast paths, tuck those checks inside the existing checks for unlikely radix_tree_deref_slot(); except for find_lock_page(), where it is an added test. And make it a BUG in find_get_pages_tag(), which is not applied to tmpfs files. A part of the reason for eliminating shmem_readpage() earlier, was to minimize the places where common code would need to allow for swap entries. The swp_entry_t known to swapfile.c must be massaged into a slightly different form when stored in the radix tree, just as it gets massaged into a pte_t when stored in page tables. In an i386 kernel this limits its information (type and page offset) to 30 bits: given 32 "types" of swapfile and 4kB pagesize, that's a maximum swapfile size of 128GB. Which is less than the 512GB we previously allowed with X86_PAE (where the swap entry can occupy the entire upper 32 bits of a pte_t), but not a new limitation on 32-bit without PAE; and there's not a new limitation on 64-bit (where swap filesize is already limited to 16TB by a 32-bit page offset). Thirty areas of 128GB is probably still enough swap for a 64GB 32-bit machine. Provide swp_to_radix_entry() and radix_to_swp_entry() conversions, and enforce filesize limit in read_swap_header(), just as for ptes. Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/swapops.h')
-rw-r--r--include/linux/swapops.h23
1 files changed, 23 insertions, 0 deletions
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index cd42e30b7c6e..2189d3ffc85d 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -1,3 +1,8 @@
+#ifndef _LINUX_SWAPOPS_H
+#define _LINUX_SWAPOPS_H
+
+#include <linux/radix-tree.h>
+
/*
* swapcache pages are stored in the swapper_space radix tree. We want to
* get good packing density in that tree, so the index should be dense in
@@ -76,6 +81,22 @@ static inline pte_t swp_entry_to_pte(swp_entry_t entry)
return __swp_entry_to_pte(arch_entry);
}
+static inline swp_entry_t radix_to_swp_entry(void *arg)
+{
+ swp_entry_t entry;
+
+ entry.val = (unsigned long)arg >> RADIX_TREE_EXCEPTIONAL_SHIFT;
+ return entry;
+}
+
+static inline void *swp_to_radix_entry(swp_entry_t entry)
+{
+ unsigned long value;
+
+ value = entry.val << RADIX_TREE_EXCEPTIONAL_SHIFT;
+ return (void *)(value | RADIX_TREE_EXCEPTIONAL_ENTRY);
+}
+
#ifdef CONFIG_MIGRATION
static inline swp_entry_t make_migration_entry(struct page *page, int write)
{
@@ -169,3 +190,5 @@ static inline int non_swap_entry(swp_entry_t entry)
return 0;
}
#endif
+
+#endif /* _LINUX_SWAPOPS_H */