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Subject[PATCH 2/4] shmem: tag swap entries in radix tree
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Shmem not uses any radix tree tags. Let's use one of them to mark
swap-entries stored in radix-tree as exceptional entries.
This allows to simplify and speedup truncate and swapoff operations.

Plus put tag manipulation, shmem_unuse(), shmem_unuse_inode() and
shmem_writepage() under CONFIG_SWAP. They are useless without swap.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
mm/shmem.c | 21 +++++++++++++++++++--
1 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 4af8e85..b8e5f90 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -76,6 +76,9 @@ static struct vfsmount *shm_mnt;
/* Symlink up to this size is kmalloc'ed instead of using a swappable page */
#define SHORT_SYMLINK_LEN 128

+/* Radix-tree tag for swap-entries */
+#define SHMEM_TAG_SWAP 0
+
struct shmem_xattr {
struct list_head list; /* anchored by shmem_inode_info->xattr_list */
char *name; /* xattr name */
@@ -239,9 +242,17 @@ static int shmem_radix_tree_replace(struct address_space *mapping,
&mapping->tree_lock);
if (item != expected)
return -ENOENT;
- if (replacement)
+ if (replacement) {
+#ifdef CONFIG_SWAP
+ if (radix_tree_exceptional_entry(replacement))
+ radix_tree_tag_set(&mapping->page_tree,
+ index, SHMEM_TAG_SWAP);
+ else if (radix_tree_exceptional_entry(expected))
+ radix_tree_tag_clear(&mapping->page_tree,
+ index, SHMEM_TAG_SWAP);
+#endif
radix_tree_replace_slot(pslot, replacement);
- else
+ } else
radix_tree_delete(&mapping->page_tree, index);
return 0;
}
@@ -592,6 +603,8 @@ static void shmem_evict_inode(struct inode *inode)
end_writeback(inode);
}

+#ifdef CONFIG_SWAP
+
/*
* If swap found in inode, free it and move page from swapcache to filecache.
*/
@@ -760,6 +773,8 @@ redirty:
return 0;
}

+#endif /* CONFIG_SWAP */
+
#ifdef CONFIG_NUMA
#ifdef CONFIG_TMPFS
static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
@@ -2281,7 +2296,9 @@ static void shmem_destroy_inodecache(void)
}

static const struct address_space_operations shmem_aops = {
+#ifdef CONFIG_SWAP
.writepage = shmem_writepage,
+#endif
.set_page_dirty = __set_page_dirty_no_writeback,
#ifdef CONFIG_TMPFS
.write_begin = shmem_write_begin,


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