Re: [PATCH] Scalable page cache

[Linus Torvalds]

In article <[e-mail]> you write:
>
>Here's the current rolled-up ext3 diff which I've been using.
>It needs to be resynced with pestiferous ext3 CVS, changelogged
>and pushed out this week.
>
>--- linux-2.4.15-pre9/fs/ext3/inode.c	Thu Nov 22 10:56:33 2001
>+++ linux-akpm/fs/ext3/inode.c	Thu Nov 22 11:07:03 2001
>@@ -1026,9 +1026,20 @@ static int ext3_prepare_write(struct fil
> 	if (ret != 0)
> 		goto prepare_write_failed;
> 
>-	if (ext3_should_journal_data(inode))
>+	if (ext3_should_journal_data(inode)) {
> 		ret = walk_page_buffers(handle, page->buffers,
> 				from, to, NULL, do_journal_get_write_access);
>+		if (ret) {
>+			/*
>+			 * We're going to fail this prepare_write(),
>+			 * so commit_write() will not be called.
>+			 * We need to undo block_prepare_write()'s kmap().
>+			 * AKPM: Do we need to clear PageUptodate?  I don't
>+			 * think so.
>+			 */
>+			kunmap(page);
>+		}
>+	}

This is wrong.

The generic VM layer does the kmap/kunmap itself these days (it really
always should have - it needs the page mapped itself for the memcpy
anyway, and depending on the low-level FS to do kmap/kunmap was an ugly
layering violation). 

So you should just remove all the kmap/kunmap stuff in
prepare/commit_write instead of adding more of them to handle the
brokenness. 

		Linus