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Subject[PATCH] swap write clustering for 2.4 (again)

Linus,

The following patch changes swap_writepage() to try to do write clustering
of phisically contiguous pages which are dirty and in the swapcache.

Do you want to include it in 2.4?


diff -Nur --exclude-from=exclude linux.orig/include/linux/mm.h linux/include/linux/mm.h
--- linux.orig/include/linux/mm.h Thu Dec 21 04:34:19 2000
+++ linux/include/linux/mm.h Thu Dec 21 03:56:30 2000
@@ -451,6 +451,8 @@
extern int filemap_swapout(struct page *, struct file *);
extern int filemap_sync(struct vm_area_struct *, unsigned long, size_t, unsigned int);
extern struct page *filemap_nopage(struct vm_area_struct *, unsigned long, int);
+extern inline struct page * ___find_page_nolock(struct address_space *, unsigned long, struct page *);
+

/*
* GFP bitmasks..
diff -Nur --exclude-from=exclude linux.orig/include/linux/swap.h linux/include/linux/swap.h
--- linux.orig/include/linux/swap.h Thu Dec 21 04:34:19 2000
+++ linux/include/linux/swap.h Thu Dec 21 04:16:42 2000
@@ -166,6 +166,8 @@
extern unsigned long swap_cache_find_total;
extern unsigned long swap_cache_find_success;
#endif
+
+extern struct swap_info_struct swap_info[MAX_SWAPFILES];

/*
* Work out if there are any other processes sharing this page, ignoring
diff -Nur --exclude-from=exclude linux.orig/mm/filemap.c linux/mm/filemap.c
--- linux.orig/mm/filemap.c Thu Dec 21 04:34:20 2000
+++ linux/mm/filemap.c Thu Dec 21 03:53:41 2000
@@ -242,7 +242,7 @@
spin_unlock(&pagecache_lock);
}

-static inline struct page * __find_page_nolock(struct address_space *mapping, unsigned long offset, struct page *page)
+inline struct page * ___find_page_nolock(struct address_space *mapping, unsigned long offset, struct page *page)
{
goto inside;

@@ -250,12 +250,22 @@
page = page->next_hash;
inside:
if (!page)
- goto not_found;
+ return NULL;
if (page->mapping != mapping)
continue;
if (page->index == offset)
break;
}
+ return page;
+}
+
+static inline struct page * __find_page_nolock(struct address_space *mapping, unsigned long offset, struct page *page)
+{
+ page = ___find_page_nolock(mapping, offset, page);
+
+ if(!page)
+ return NULL;
+
/*
* Touching the page may move it to the active list.
* If we end up with too few inactive pages, we wake
@@ -264,7 +274,7 @@
age_page_up(page);
if (inactive_shortage() > inactive_target / 2 && free_shortage())
wakeup_kswapd(0);
-not_found:
+
return page;
}

diff -Nur --exclude-from=exclude linux.orig/mm/swap_state.c linux/mm/swap_state.c
--- linux.orig/mm/swap_state.c Mon Dec 4 19:22:02 2000
+++ linux/mm/swap_state.c Thu Dec 21 04:23:47 2000
@@ -5,6 +5,8 @@
* Swap reorganised 29.12.95, Stephen Tweedie
*
* Rewritten to use page cache, (C) 1998 Stephen Tweedie
+ *
+ * 21/12/2000 Added swap write clustering. Marcelo Tosatti
*/

#include <linux/mm.h>
@@ -17,9 +19,95 @@

#include <asm/pgtable.h>

+static inline struct page * swap_page_dirty(unsigned long, unsigned long, struct swap_info_struct *);
+
+#define SWAP_WRITE_CLUSTER (1 << page_cluster)
+
static int swap_writepage(struct page *page)
{
- rw_swap_page(WRITE, page, 0);
+ unsigned long page_offset, curr, offset, i, type;
+ struct swap_info_struct *swap;
+ swp_entry_t entry;
+ struct page *cpages[SWAP_WRITE_CLUSTER*2];
+ int count, first;
+
+ entry.val = page->index;
+
+ type = SWP_TYPE(entry);
+
+ swap = &swap_info[type];
+
+ /* If swap area is not a real device, do not try to write cluster. */
+ if(!swap->swap_device) {
+ rw_swap_page(WRITE, page, 0);
+ return 0;
+ }
+
+ page_offset = offset = SWP_OFFSET(entry);
+ cpages[SWAP_WRITE_CLUSTER] = page;
+ count = 1;
+ first = SWAP_WRITE_CLUSTER;
+ curr = 1;
+
+ spin_lock(&pagecache_lock);
+ swap_device_lock(swap);
+
+ /*
+ * Search for clusterable dirty swap pages.
+ */
+
+ while (count < SWAP_WRITE_CLUSTER) {
+ struct page *p = NULL;
+
+ if(offset <= 0)
+ break;
+
+ offset = page_offset - curr;
+ p = swap_page_dirty(offset, type, swap);
+
+ if(!p)
+ break;
+
+ cpages[--first] = p;
+
+ ClearPageDirty(p);
+ curr++;
+ count++;
+ }
+
+ curr = 1;
+
+ while (count < SWAP_WRITE_CLUSTER) {
+ struct page *p = NULL;
+ offset = page_offset + curr;
+
+ if(offset >= swap->max)
+ break;
+
+ p = swap_page_dirty(offset, type, swap);
+ if(!p)
+ break;
+
+ cpages[first + count] = p;
+ ClearPageDirty(p);
+ curr++;
+ count++;
+ }
+
+ swap_device_unlock(swap);
+ spin_unlock(&pagecache_lock);
+
+ /* Now write out everything we were able to cluster */
+
+ for(i=0; i<count; i++) {
+ int pos = first + i;
+ rw_swap_page(WRITE, cpages[pos], 0);
+
+ /* If the page is a clustered one, decrement its counter */
+ if(pos != SWAP_WRITE_CLUSTER)
+ page_cache_release(cpages[pos]);
+ }
+
return 0;
}

@@ -36,6 +124,43 @@
0, /* nrpages */
&swap_aops,
};
+
+static inline struct page * swap_page_dirty(unsigned long offset, unsigned long type,
+ struct swap_info_struct *swapdev)
+{
+ struct page *page, **hash;
+ swp_entry_t entry;
+ unsigned long index;
+
+ entry = SWP_ENTRY(type, offset);
+
+ index = entry.val;
+
+ if(!swapdev->swap_map[offset])
+ return NULL;
+
+ if(swapdev->swap_map[offset] == SWAP_MAP_BAD)
+ return NULL;
+
+ hash = page_hash(&swapper_space, index);
+
+ page = ___find_page_nolock(&swapper_space, index, *hash);
+
+ if(!page)
+ return NULL;
+
+ if(TryLockPage(page))
+ return NULL;
+
+ page_cache_get(page);
+
+ if(PageDirty(page) && PageSwapCache(page))
+ return page;
+
+ UnlockPage(page);
+ page_cache_release(page);
+ return NULL;
+}

#ifdef SWAP_CACHE_INFO
unsigned long swap_cache_add_total;

-
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