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Message-ID: <20080602095222.GA9225@skywalker>
Date: Mon, 2 Jun 2008 15:22:22 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To: Jan Kara <jack@...e.cz>
Cc: cmm@...ibm.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Add validation to jbd lock inversion patch and
split and writepage
Hi Jan,
On Mon, Jun 02, 2008 at 11:31:06AM +0200, Jan Kara wrote:
> Hi Aneesh,
>
> Thanks for the patch but I though we decided to do this a bit differently -
> see below.
Please feel free to merge the changes back to the lock inversion
patches. I sent it as a separate the patches to make it easier for review.
>
> On Fri 30-05-08 19:09:27, Aneesh Kumar K.V wrote:
> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> > ---
> > fs/ext4/inode.c | 181 +++++++++++++++++++++++++++++++++++++++++++++++--------
> > 1 files changed, 156 insertions(+), 25 deletions(-)
> >
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index a96c325..b122425 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -1479,6 +1479,11 @@ static int jbd2_journal_dirty_data_fn(handle_t *handle, struct buffer_head *bh)
> > return 0;
> > }
> >
> > +static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
> > +{
> > + return (!buffer_mapped(bh) || buffer_delay(bh));
> > +}
> > +
> > /*
> > * Note that we don't need to start a transaction unless we're journaling
> > * data because we should have holes filled from ext4_page_mkwrite(). If
> > @@ -1531,18 +1536,26 @@ static int jbd2_journal_dirty_data_fn(handle_t *handle, struct buffer_head *bh)
> > static int __ext4_ordered_writepage(struct page *page,
> > struct writeback_control *wbc)
> > {
> > - struct inode *inode = page->mapping->host;
> > - struct buffer_head *page_bufs;
> > + int ret = 0, err;
> > + unsigned long len;
> > handle_t *handle = NULL;
> > - int ret = 0;
> > - int err;
> > + struct buffer_head *page_bufs;
> > + struct inode *inode = page->mapping->host;
> > + loff_t size = i_size_read(inode);
> >
> > - if (!page_has_buffers(page)) {
> > - create_empty_buffers(page, inode->i_sb->s_blocksize,
> > - (1 << BH_Dirty)|(1 << BH_Uptodate));
> > - }
> This is OK.
>
> > page_bufs = page_buffers(page);
> > - walk_page_buffers(handle, page_bufs, 0,
> > + if (page->index == size >> PAGE_CACHE_SHIFT)
> > + len = size & ~PAGE_CACHE_MASK;
> > + else
> > + len = PAGE_CACHE_SIZE;
> > +
> > + if (walk_page_buffers(NULL, page_bufs, 0,
> > + len, NULL, ext4_bh_unmapped_or_delay)) {
> > + printk(KERN_CRIT "%s called with unmapped or delay buffer\n",
> > + __func__);
> > + BUG();
> > + }
> But I'd move this check to ext4_ordered_writepage().
>
Please feel free to do so. The only reason for me to do it as a separate
function is to clarify that with the changes writepage doesn't do any
block allocation at all. And calling writepage via page_mkwrite goes
against that. So i renamed the page_mkwrite call out to *_allocpage
and made sure writepage doesn't do any block allocation.
> > + walk_page_buffers(NULL, page_bufs, 0,
> > PAGE_CACHE_SIZE, NULL, bget_one);
> >
[.... snip ..... ]
> >
> > + if (walk_page_buffers(NULL, page_bufs, 0,
> > + len, NULL, ext4_bh_unmapped_or_delay)) {
> > + printk(KERN_CRIT "%s called with unmapped or delay buffer\n",
> > + __func__);
> > + BUG();
> > + }
> > + /* FIXME!! do we need to call prepare_write for a mapped buffer */
> This can go to ext4_journalled_writepage(). What is actually this FIXME
> about? I'm not sure I get it...
>
I was wondering whether we need to call prepare_write in writepage ?. We
are not allocating any new blocks in writepage with these changes.
> > ret = block_prepare_write(page, 0, PAGE_CACHE_SIZE, ext4_get_block);
> > if (ret != 0)
> > goto out_unlock;
> >
> > - page_bufs = page_buffers(page);
> > walk_page_buffers(handle, page_bufs, 0, PAGE_CACHE_SIZE, NULL,
> > bget_one);
> > /* As soon as we unlock the page, it can go away, but we have
> > @@ -1671,14 +1713,13 @@ static int __ext4_journalled_writepage(struct page *page,
> > static int ext4_journalled_writepage(struct page *page,
> > struct writeback_control *wbc)
> > {
> > + BUG_ON(!page_has_buffers(page));
> > +
> > if (ext4_journal_current_handle())
> > goto no_write;
> >
> > - if (!page_has_buffers(page) || PageChecked(page)) {
> > - /*
> > - * It's mmapped pagecache. Add buffers and journal it. There
> > - * doesn't seem much point in redirtying the page here.
> > - */
> > + if (PageChecked(page)) {
> > + /* dirty pages in data=journal mode */
> > ClearPageChecked(page);
> > return __ext4_journalled_writepage(page, wbc);
> > } else {
> > @@ -3520,6 +3561,96 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
> > return err;
> > }
> >
> > +static int __ext4_journalled_allocpage(struct page *page,
> > + struct writeback_control *wbc)
> > +{
> > + int ret = 0, err;
> > + handle_t *handle = NULL;
> > + struct address_space *mapping = page->mapping;
> > + struct inode *inode = mapping->host;
> > + struct buffer_head *page_bufs;
> > +
> > + /* if alloc we are called after statring a journal */
> > + handle = ext4_journal_current_handle();
> > + BUG_ON(!handle);
> > +
> > + ret = block_prepare_write(page, 0, PAGE_CACHE_SIZE, ext4_get_block);
> > + if (ret != 0)
> > + goto out_unlock;
> > +
> > + /* FIXME!! should we do a bget_one */
> > + page_bufs = page_buffers(page);
> > + ret = walk_page_buffers(handle, page_bufs, 0,
> > + PAGE_CACHE_SIZE, NULL, do_journal_get_write_access);
> > +
I also have a FIXME here. I am not sure whether unlocking the page have
some effect. Can you verify this ?
> > + err = walk_page_buffers(handle, page_bufs, 0,
> > + PAGE_CACHE_SIZE, NULL, write_end_fn);
> > + if (ret == 0)
> > + ret = err;
> > + EXT4_I(inode)->i_state |= EXT4_STATE_JDATA;
> > +
> > +out_unlock:
> > + unlock_page(page);
> > + return ret;
> > +}
> > +
-aneesh
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