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Commit 21d31f1f authored by Joern Engel's avatar Joern Engel
Browse files

[PATCH] [MTD] block2mtd: remove readahead code 



Over the years there was a slow trickle of complaints against the readahead
code.  Most of them concerned performance, Peter Zijlstra stumbled over it
when working unrelated changes and I believe there was an actual bug report.
Oh, Andrew Morton also complained about duplicating code from mm/readahead.c.

It is just not worth it.  On flash media like usb sticks, readahead will
make things go slow - very slow.  On spinning disks, readahead may be a
win, but this is definitely not the place to add it.

Signed-off-by: default avatarJörn Engel <joern@lazybastard.org>
parent 8870530a

drivers/mtd/devices/block2mtd.c

+4 −53
Original line number Diff line number Diff line
@@ -40,56 +40,9 @@ struct block2mtd_dev { 
static LIST_HEAD(blkmtd_device_list);





#define PAGE_READAHEAD 64

static void cache_readahead(struct address_space *mapping, int index)

static struct page* page_read(struct address_space *mapping, int index)

{

	filler_t *filler = (filler_t*)mapping->a_ops->readpage;

	int i, pagei;

	unsigned ret = 0;

	unsigned long end_index;

	struct page *page;

	LIST_HEAD(page_pool);

	struct inode *inode = mapping->host;

	loff_t isize = i_size_read(inode);



	if (!isize) {

		INFO("iSize=0 in cache_readahead\n");

		return;

	}



	end_index = ((isize - 1) >> PAGE_CACHE_SHIFT);



	read_lock_irq(&mapping->tree_lock);

	for (i = 0; i < PAGE_READAHEAD; i++) {

		pagei = index + i;

		if (pagei > end_index) {

			INFO("Overrun end of disk in cache readahead\n");

			break;

		}

		page = radix_tree_lookup(&mapping->page_tree, pagei);

		if (page && (!i))

			break;

		if (page)

			continue;

		read_unlock_irq(&mapping->tree_lock);

		page = page_cache_alloc_cold(mapping);

		read_lock_irq(&mapping->tree_lock);

		if (!page)

			break;

		page->index = pagei;

		list_add(&page->lru, &page_pool);

		ret++;

	}

	read_unlock_irq(&mapping->tree_lock);

	if (ret)

		read_cache_pages(mapping, &page_pool, filler, NULL);

}





static struct page* page_readahead(struct address_space *mapping, int index)

{

	filler_t *filler = (filler_t*)mapping->a_ops->readpage;

	cache_readahead(mapping, index);

	return read_cache_page(mapping, index, filler, NULL);

}
@@ -105,7 +58,7 @@ static int _block2mtd_erase(struct block2mtd_dev *dev, loff_t to, size_t len) 
	u_long *max;



	while (pages) {

		page = page_readahead(mapping, index);

		page = page_read(mapping, index);

		if (!page)

			return -ENOMEM;

		if (IS_ERR(page))
@@ -174,8 +127,7 @@ static int block2mtd_read(struct mtd_info *mtd, loff_t from, size_t len, 
			cpylen = len;	// this page

		len = len - cpylen;



		//      Get page

		page = page_readahead(dev->blkdev->bd_inode->i_mapping, index);

		page = page_read(dev->blkdev->bd_inode->i_mapping, index);

		if (!page)

			return -ENOMEM;

		if (IS_ERR(page))
@@ -213,8 +165,7 @@ static int _block2mtd_write(struct block2mtd_dev *dev, const u_char *buf, 
			cpylen = len;			// this page

		len = len - cpylen;



		//	Get page

		page = page_readahead(mapping, index);

		page = page_read(mapping, index);

		if (!page)

			return -ENOMEM;

		if (IS_ERR(page))