Re: Lockless page cache test results

Nick Piggin
2006-04-30T13:38:20Z

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Jens Axboe wrote:

> You killed a lock too many there. I'm sure it'd help scalability,
> though :-)

Ssshh! That was my secret plan :)

Good catch though, thanks. I'll attach a new patch in case David
has a chance to try it out.

--
SUSE Labs, Novell Inc.

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Index: linux-2.6/fs/mpage.c
===================================================================
--- linux-2.6.orig/fs/mpage.c 2006-04-30 19:36:18.000000000 +1000
+++ linux-2.6/fs/mpage.c 2006-04-30 21:42:15.000000000 +1000
@@ -26,6 +26,7 @@
#include <linux/writeback.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
+#include <linux/swap.h>

/*
* I/O completion handler for multipage BIOs.
@@ -389,31 +390,57 @@ mpage_readpages(struct address_space *ma
struct bio *bio = NULL;
unsigned page_idx;
sector_t last_block_in_bio = 0;
- struct pagevec lru_pvec;
+ struct pagevec pvec;
struct buffer_head map_bh;
unsigned long first_logical_block = 0;

clear_buffer_mapped(&map_bh);
- pagevec_init(&lru_pvec, 0);
+ pagevec_init(&pvec, 0);
for (page_idx = 0; page_idx < nr_pages; page_idx++) {
struct page *page = list_entry(pages->prev, struct page, lru);

prefetchw(&page->flags);
list_del(&page->lru);
- if (!add_to_page_cache(page, mapping,
- page->index, GFP_KERNEL)) {
- bio = do_mpage_readpage(bio, page,
- nr_pages - page_idx,
- &last_block_in_bio, &map_bh,
- &first_logical_block,
- get_block);
- if (!pagevec_add(&lru_pvec, page))
- __pagevec_lru_add(&lru_pvec);
- } else {
- page_cache_release(page);
+
+ if (!pagevec_add(&pvec, page) || page_idx == nr_pages-1) {
+ int i = 0, in_cache;
+
+ if (radix_tree_preload(GFP_KERNEL))
+ goto pagevec_error;
+
+ write_lock_irq(&mapping->tree_lock);
+ for (; i < pagevec_count(&pvec); i++) {
+ struct page *page = pvec.pages[i];
+ unsigned long offset = page->index;
+
+ if (__add_to_page_cache(page, mapping, offset))
+ break; /* error */
+ }
+ write_unlock_irq(&mapping->tree_lock);
+ radix_tree_preload_end();
+
+ in_cache = i;
+ for (i = 0; i < in_cache; i++) {
+ struct page *page = pvec.pages[i];
+
+ bio = do_mpage_readpage(bio, page,
+ nr_pages - page_idx,
+ &last_block_in_bio, &map_bh,
+ &first_logical_block,
+ get_block);
+ lru_cache_add(page);
+ }
+
+pagevec_error:
+ for (; i < pagevec_count(&pvec); i++) {
+ struct page *page = pvec.pages[i];
+ page_cache_release(page);
+ }
+
+ pagevec_reinit(&pvec);
}
}
- pagevec_lru_add(&lru_pvec);
+
BUG_ON(!list_empty(pages));
if (bio)
mpage_bio_submit(READ, bio);
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c 2006-04-30 19:36:18.000000000 +1000
+++ linux-2.6/mm/filemap.c 2006-04-30 21:42:42.000000000 +1000
@@ -394,6 +394,21 @@ int filemap_write_and_wait_range(struct
return err;
}

+int __add_to_page_cache(struct page *page, struct address_space *mapping,
+ pgoff_t offset)
+{
+ int error = radix_tree_insert(&mapping->page_tree, offset, page);
+ if (!error) {
+ page_cache_get(page);
+ SetPageLocked(page);
+ page->mapping = mapping;
+ page->index = offset;
+ mapping->nrpages++;
+ pagecache_acct(1);
+ }
+ return error;
+}
+
/*
* This function is used to add newly allocated pagecache pages:
* the page is new, so we can just run SetPageLocked() against it.
@@ -408,18 +423,11 @@ int add_to_page_cache(struct page *page,

if (error == 0) {
write_lock_irq(&mapping->tree_lock);
- error = radix_tree_insert(&mapping->page_tree, offset, page);
- if (!error) {
- page_cache_get(page);
- SetPageLocked(page);
- page->mapping = mapping;
- page->index = offset;
- mapping->nrpages++;
- pagecache_acct(1);
- }
+ error = __add_to_page_cache(page, mapping, offset);
write_unlock_irq(&mapping->tree_lock);
radix_tree_preload_end();
}
+
return error;
}

Index: linux-2.6/mm/readahead.c
===================================================================
--- linux-2.6.orig/mm/readahead.c 2006-04-30 19:36:18.000000000 +1000
+++ linux-2.6/mm/readahead.c 2006-04-30 21:42:15.000000000 +1000
@@ -14,6 +14,7 @@
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/pagevec.h>
+#include <linux/swap.h>

void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
{
@@ -164,37 +165,60 @@ int read_cache_pages(struct address_spac

EXPORT_SYMBOL(read_cache_pages);

-static int read_pages(struct address_space *mapping, struct file *filp,
+static void __pagevec_read_pages(struct file *filp,
+ struct address_space *mapping, struct pagevec *pvec)
+{
+ int i = 0, in_cache;
+
+ if (radix_tree_preload(GFP_KERNEL))
+ goto out_error;
+
+ write_lock_irq(&mapping->tree_lock);
+ for (; i < pagevec_count(pvec); i++) {
+ struct page *page = pvec->pages[i];
+ unsigned long offset = page->index;
+
+ if (__add_to_page_cache(page, mapping, offset))
+ break; /* error */
+ }
+ write_unlock_irq(&mapping->tree_lock);
+ radix_tree_preload_end();
+
+ in_cache = i;
+ for (i = 0; i < in_cache; i++) {
+ struct page *page = pvec->pages[i];
+ mapping->a_ops->readpage(filp, page);
+ lru_cache_add(page);
+ }
+
+out_error:
+ for (; i < pagevec_count(pvec); i++) {
+ struct page *page = pvec->pages[i];
+ page_cache_release(page);
+ }
+
+ pagevec_reinit(pvec);
+}
+
+static void read_pages(struct address_space *mapping, struct file *filp,
struct list_head *pages, unsigned nr_pages)
{
- unsigned page_idx;
- struct pagevec lru_pvec;
- int ret;
+ unsigned i;
+ struct pagevec pvec;

if (mapping->a_ops->readpages) {
- ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
- goto out;
+ mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
+ return;
}

- pagevec_init(&lru_pvec, 0);
- for (page_idx = 0; page_idx < nr_pages; page_idx++) {
+ pagevec_init(&pvec, 0);
+ for (i = 0; i < nr_pages; i++) {
struct page *page = list_to_page(pages);
list_del(&page->lru);
- if (!add_to_page_cache(page, mapping,
- page->index, GFP_KERNEL)) {
- ret = mapping->a_ops->readpage(filp, page);
- if (ret != AOP_TRUNCATED_PAGE) {
- if (!pagevec_add(&lru_pvec, page))
- __pagevec_lru_add(&lru_pvec);
- continue;
- } /* else fall through to release */
- }
- page_cache_release(page);
+
+ if (!pagevec_add(&pvec, page) || i == nr_pages-1)
+ __pagevec_read_pages(filp, mapping, &pvec);
}
- pagevec_lru_add(&lru_pvec);
- ret = 0;
-out:
- return ret;
}

/*
Index: linux-2.6/include/linux/pagemap.h
===================================================================
--- linux-2.6.orig/include/linux/pagemap.h 2006-04-30 19:36:18.000000000 +1000
+++ linux-2.6/include/linux/pagemap.h 2006-04-30 21:42:16.000000000 +1000
@@ -97,6 +97,8 @@ extern struct page * read_cache_page(str
extern int read_cache_pages(struct address_space *mapping,
struct list_head *pages, filler_t *filler, void *data);

+int __add_to_page_cache(struct page *page, struct address_space *mapping,
+ unsigned long index);
int add_to_page_cache(struct page *page, struct address_space *mapping,
unsigned long index, gfp_t gfp_mask);
int add_to_page_cache_lru(struct page *page, struct address_space *mapping,