Re: [PATCH] mm: remove global locks from mm/highmem.c

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jan 31, 2007 at 02:22:24PM +1100, David Chinner wrote:
> > Yup.  Even better, use clear_highpage().
> 
> For even more goodness, clearmem_highpage_flush() does exactly
> the right thing for partial page zeroing ;)

Note that there are tons of places in buffer.c that could use
clearmem_highpage_flush().  See the so far untested patch below:


Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c	2007-02-02 12:53:51.000000000 +0100
+++ linux-2.6/fs/buffer.c	2007-02-02 12:59:42.000000000 +0100
@@ -1858,13 +1858,8 @@
 		if (block_start >= to)
 			break;
 		if (buffer_new(bh)) {
-			void *kaddr;
-
 			clear_buffer_new(bh);
-			kaddr = kmap_atomic(page, KM_USER0);
-			memset(kaddr+block_start, 0, bh->b_size);
-			flush_dcache_page(page);
-			kunmap_atomic(kaddr, KM_USER0);
+			memclear_highpage_flush(page, block_start, bh->b_size);
 			set_buffer_uptodate(bh);
 			mark_buffer_dirty(bh);
 		}
@@ -1952,10 +1947,8 @@
 					SetPageError(page);
 			}
 			if (!buffer_mapped(bh)) {
-				void *kaddr = kmap_atomic(page, KM_USER0);
-				memset(kaddr + i * blocksize, 0, blocksize);
-				flush_dcache_page(page);
-				kunmap_atomic(kaddr, KM_USER0);
+				memclear_highpage_flush(page, i * blocksize,
+							blocksize);
 				if (!err)
 					set_buffer_uptodate(bh);
 				continue;
@@ -2098,7 +2091,6 @@
 	long status;
 	unsigned zerofrom;
 	unsigned blocksize = 1 << inode->i_blkbits;
-	void *kaddr;
 
 	while(page->index > (pgpos = *bytes>>PAGE_CACHE_SHIFT)) {
 		status = -ENOMEM;
@@ -2120,10 +2112,8 @@
 						PAGE_CACHE_SIZE, get_block);
 		if (status)
 			goto out_unmap;
-		kaddr = kmap_atomic(new_page, KM_USER0);
-		memset(kaddr+zerofrom, 0, PAGE_CACHE_SIZE-zerofrom);
-		flush_dcache_page(new_page);
-		kunmap_atomic(kaddr, KM_USER0);
+		memclear_highpage_flush(page, zerofrom,
+					PAGE_CACHE_SIZE - zerofrom);
 		generic_commit_write(NULL, new_page, zerofrom, PAGE_CACHE_SIZE);
 		unlock_page(new_page);
 		page_cache_release(new_page);
@@ -2150,10 +2140,7 @@
 	if (status)
 		goto out1;
 	if (zerofrom < offset) {
-		kaddr = kmap_atomic(page, KM_USER0);
-		memset(kaddr+zerofrom, 0, offset-zerofrom);
-		flush_dcache_page(page);
-		kunmap_atomic(kaddr, KM_USER0);
+		memclear_highpage_flush(page, zerofrom, offset - zerofrom);
 		__block_commit_write(inode, page, zerofrom, offset);
 	}
 	return 0;
@@ -2368,10 +2355,7 @@
 	 * Error recovery is pretty slack.  Clear the page and mark it dirty
 	 * so we'll later zero out any blocks which _were_ allocated.
 	 */
-	kaddr = kmap_atomic(page, KM_USER0);
-	memset(kaddr, 0, PAGE_CACHE_SIZE);
-	flush_dcache_page(page);
-	kunmap_atomic(kaddr, KM_USER0);
+	memclear_highpage_flush(page, 0, PAGE_CACHE_SIZE);
 	SetPageUptodate(page);
 	set_page_dirty(page);
 	return ret;
@@ -2405,7 +2389,6 @@
 	loff_t i_size = i_size_read(inode);
 	const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
 	unsigned offset;
-	void *kaddr;
 	int ret;
 
 	/* Is the page fully inside i_size? */
@@ -2436,10 +2419,7 @@
 	 * the  page size, the remaining memory is zeroed when mapped, and
 	 * writes to that region are not written out to the file."
 	 */
-	kaddr = kmap_atomic(page, KM_USER0);
-	memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
-	flush_dcache_page(page);
-	kunmap_atomic(kaddr, KM_USER0);
+	memclear_highpage_flush(page, offset, PAGE_CACHE_SIZE - offset);
 out:
 	ret = mpage_writepage(page, get_block, wbc);
 	if (ret == -EAGAIN)
@@ -2460,7 +2440,6 @@
 	unsigned to;
 	struct page *page;
 	const struct address_space_operations *a_ops = mapping->a_ops;
-	char *kaddr;
 	int ret = 0;
 
 	if ((offset & (blocksize - 1)) == 0)
@@ -2474,10 +2453,7 @@
 	to = (offset + blocksize) & ~(blocksize - 1);
 	ret = a_ops->prepare_write(NULL, page, offset, to);
 	if (ret == 0) {
-		kaddr = kmap_atomic(page, KM_USER0);
-		memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
-		flush_dcache_page(page);
-		kunmap_atomic(kaddr, KM_USER0);
+		memclear_highpage_flush(page, offset, PAGE_CACHE_SIZE - offset);
 		set_page_dirty(page);
 	}
 	unlock_page(page);
@@ -2498,7 +2474,6 @@
 	struct inode *inode = mapping->host;
 	struct page *page;
 	struct buffer_head *bh;
-	void *kaddr;
 	int err;
 
 	blocksize = 1 << inode->i_blkbits;
@@ -2552,11 +2527,7 @@
 			goto unlock;
 	}
 
-	kaddr = kmap_atomic(page, KM_USER0);
-	memset(kaddr + offset, 0, length);
-	flush_dcache_page(page);
-	kunmap_atomic(kaddr, KM_USER0);
-
+	memclear_highpage_flush(page, offset, length);
 	mark_buffer_dirty(bh);
 	err = 0;
 
@@ -2577,7 +2548,6 @@
 	loff_t i_size = i_size_read(inode);
 	const pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
 	unsigned offset;
-	void *kaddr;
 
 	/* Is the page fully inside i_size? */
 	if (page->index < end_index)
@@ -2603,10 +2573,7 @@
 	 * the  page size, the remaining memory is zeroed when mapped, and
 	 * writes to that region are not written out to the file."
 	 */
-	kaddr = kmap_atomic(page, KM_USER0);
-	memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
-	flush_dcache_page(page);
-	kunmap_atomic(kaddr, KM_USER0);
+	memclear_highpage_flush(page, offset, PAGE_CACHE_SIZE - offset);
 	return __block_write_full_page(inode, page, get_block, wbc);
 }
 

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