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Subject[PATCH] tmpfs 4/4 swapoff tweaks
Several simple speedups to tmpfs swapoff: without patch, swapoff of a
kernel tree in tmpfs might take take 2 minutes, with patch 4 seconds.
Inline search go no further than necessary; only search inode when it
has swapped pages; start next search from same inode; list in order.

--- 2.4.19-pre10/mm/shmem.c Tue Jun 11 19:02:30 2002
+++ linux/mm/shmem.c Tue Jun 11 19:02:30 2002
@@ -372,28 +372,30 @@
clear_inode(inode);
}

-static int shmem_clear_swp (swp_entry_t entry, swp_entry_t *ptr, int size) {
+static inline int shmem_find_swp(swp_entry_t entry, swp_entry_t *ptr, swp_entry_t *eptr)
+{
swp_entry_t *test;

- for (test = ptr; test < ptr + size; test++) {
- if (test->val == entry.val) {
- swap_free (entry);
- *test = (swp_entry_t) {0};
+ for (test = ptr; test < eptr; test++) {
+ if (test->val == entry.val)
return test - ptr;
- }
}
return -1;
}

-static int shmem_unuse_inode (struct shmem_inode_info *info, swp_entry_t entry, struct page *page)
+static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, struct page *page)
{
swp_entry_t *ptr;
unsigned long idx;
int offset;
-
+
idx = 0;
+ ptr = info->i_direct;
spin_lock (&info->lock);
- offset = shmem_clear_swp (entry, info->i_direct, SHMEM_NR_DIRECT);
+ offset = info->next_index;
+ if (offset > SHMEM_NR_DIRECT)
+ offset = SHMEM_NR_DIRECT;
+ offset = shmem_find_swp(entry, ptr, ptr + offset);
if (offset >= 0)
goto found;

@@ -402,13 +404,18 @@
ptr = shmem_swp_entry(info, idx, 0);
if (IS_ERR(ptr))
continue;
- offset = shmem_clear_swp (entry, ptr, ENTRIES_PER_PAGE);
+ offset = info->next_index - idx;
+ if (offset > ENTRIES_PER_PAGE)
+ offset = ENTRIES_PER_PAGE;
+ offset = shmem_find_swp(entry, ptr, ptr + offset);
if (offset >= 0)
goto found;
}
spin_unlock (&info->lock);
return 0;
found:
+ swap_free(entry);
+ ptr[offset] = (swp_entry_t) {0};
delete_from_swap_cache(page);
add_to_page_cache(page, info->inode->i_mapping, offset + idx);
SetPageDirty(page);
@@ -419,7 +426,7 @@
}

/*
- * unuse_shmem() search for an eventually swapped out shmem page.
+ * shmem_unuse() search for an eventually swapped out shmem page.
*/
void shmem_unuse(swp_entry_t entry, struct page *page)
{
@@ -430,8 +437,12 @@
list_for_each(p, &shmem_inodes) {
info = list_entry(p, struct shmem_inode_info, list);

- if (shmem_unuse_inode(info, entry, page))
+ if (info->swapped && shmem_unuse_inode(info, entry, page)) {
+ /* move head to start search for next from here */
+ list_del(&shmem_inodes);
+ list_add_tail(&shmem_inodes, p);
break;
+ }
}
spin_unlock (&shmem_ilock);
}
@@ -721,7 +732,7 @@
inode->i_op = &shmem_inode_operations;
inode->i_fop = &shmem_file_operations;
spin_lock (&shmem_ilock);
- list_add (&SHMEM_I(inode)->list, &shmem_inodes);
+ list_add_tail(&SHMEM_I(inode)->list, &shmem_inodes);
spin_unlock (&shmem_ilock);
break;
case S_IFDIR:
@@ -1163,7 +1174,7 @@
}
inode->i_op = &shmem_symlink_inode_operations;
spin_lock (&shmem_ilock);
- list_add (&info->list, &shmem_inodes);
+ list_add_tail(&info->list, &shmem_inodes);
spin_unlock (&shmem_ilock);
down(&info->sem);
page = shmem_getpage_locked(info, inode, 0);
-
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