linux-kernel - RE: [PATCH] udf: avoid redundant memcpy when writing data in ICB

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Date:	Mon, 14 Jul 2014 19:14:39 +0800
From:	Chao Yu <chao2.yu@...sung.com>
To:	'Jan Kara' <jack@...e.cz>
Cc:	linux-kernel@...r.kernel.org
Subject: RE: [PATCH] udf: avoid redundant memcpy when writing data in ICB

> -----Original Message-----
> From: Jan Kara [mailto:jack@...e.cz]
> Sent: Monday, July 14, 2014 4:46 PM
> To: Chao Yu
> Cc: jack@...e.cz; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] udf: avoid redundant memcpy when writing data in ICB
> 
> On Mon 30-06-14 13:37:15, Chao Yu wrote:
> > We have already copied the changed data of page to extent area in ICB when call
> > ->write_end() of adinicb aops, so we do not need to copy them another time in
> > ->writepage() of adinicb aops. SetPageUptodate is redundant too, so it's better
> > to remove these redundant codes.
> >
> > Also it looks more reasonable to set inode dirty after extent area are modified,
> > we'd better move mark_inode_dirty() from ->writepage() to ->write_end().
>   This doesn't look right. The copy is there because the page can be
> modified via mmap as well, not only via buffered write... So if anything,

You're right, I have made a mistake that I have not considered the 'mmap' case,
Thank you for reminding me about that. :)

> we may be able to remove the copy in udf_adinicb_write_end() (actually
> using directly simple_write_end() for that), not the one in
> udf_adinicb_write_begin().

Agreed, valid data within i_size will be copied to ICB cache when we writeback
the page by invoking udf_adinicb_writepage, so the copy in udf_adinicb_write_end
is redundant. So our patch should be modified like the following one, is this right?

---
 fs/udf/file.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/fs/udf/file.c b/fs/udf/file.c
index d80738f..a8dc0f1 100644
--- a/fs/udf/file.c
+++ b/fs/udf/file.c
@@ -105,16 +105,6 @@ static int udf_adinicb_write_end(struct file *file,
 			loff_t pos, unsigned len, unsigned copied,
 			struct page *page, void *fsdata)
 {
-	struct inode *inode = mapping->host;
-	unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
-	char *kaddr;
-	struct udf_inode_info *iinfo = UDF_I(inode);
-
-	kaddr = kmap_atomic(page);
-	memcpy(iinfo->i_ext.i_data + iinfo->i_lenEAttr + offset,
-		kaddr + offset, copied);
-	kunmap_atomic(kaddr);
-
 	return simple_write_end(file, mapping, pos, len, copied, page, fsdata);
 }
 
-- 
2.0.1.474.g72c7794


> 
> 								Honza
> >
> > Signed-off-by: Chao Yu <chao2.yu@...sung.com>
> > ---
> >  fs/udf/file.c |   12 ++----------
> >  1 file changed, 2 insertions(+), 10 deletions(-)
> >
> > diff --git a/fs/udf/file.c b/fs/udf/file.c
> > index d80738f..3cd0a50 100644
> > --- a/fs/udf/file.c
> > +++ b/fs/udf/file.c
> > @@ -65,17 +65,7 @@ static int udf_adinicb_readpage(struct file *file, struct page *page)
> >  static int udf_adinicb_writepage(struct page *page,
> >  				 struct writeback_control *wbc)
> >  {
> > -	struct inode *inode = page->mapping->host;
> > -	char *kaddr;
> > -	struct udf_inode_info *iinfo = UDF_I(inode);
> > -
> >  	BUG_ON(!PageLocked(page));
> > -
> > -	kaddr = kmap(page);
> > -	memcpy(iinfo->i_ext.i_data + iinfo->i_lenEAttr, kaddr, inode->i_size);
> > -	mark_inode_dirty(inode);
> > -	SetPageUptodate(page);
> > -	kunmap(page);
> >  	unlock_page(page);
> >
> >  	return 0;
> > @@ -115,6 +105,8 @@ static int udf_adinicb_write_end(struct file *file,
> >  		kaddr + offset, copied);
> >  	kunmap_atomic(kaddr);
> >
> > +	mark_inode_dirty(inode);
> > +
> >  	return simple_write_end(file, mapping, pos, len, copied, page, fsdata);
> >  }
> >
> > --
> > 1.7.9.5
> >
> >
> --
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR

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