Re: Re: [PATCH 1/5] mm/readahead: Check return value of read_pages

[Raghavendra D Prabhu <raghu.prabhu13@xxxxxxxxx>]

Hi,


* On Sat, Sep 22, 2012 at 08:43:37PM +0800, Fengguang Wu <fengguang.wu@xxxxxxxxx> wrote:
> On Sat, Sep 22, 2012 at 04:03:10PM +0530, raghu.prabhu13@xxxxxxxxx wrote:
> > From: Raghavendra D Prabhu <rprabhu@xxxxxxxxxxx>
> >
> > Return value of a_ops->readpage will be propagated to return value of read_pages
> > and __do_page_cache_readahead.
>
> That does not explain the intention and benefit of this patch..

I noticed that force_page_cache_readahead checks return value of 
__do_page_cache_readahead but the actual error if any is never 
propagated.


Also, I made a slight change there:


+	int alloc = 1;
 
 	blk_start_plug(&plug);
 
@@ -127,13 +128,18 @@ static int read_pages(struct address_space *mapping, struct file *filp,
 	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
 		struct page *page = list_to_page(pages);
 		list_del(&page->lru);
-		if (!add_to_page_cache_lru(page, mapping,
+		if (alloc && !add_to_page_cache_lru(page, mapping,
 					page->index, GFP_KERNEL)) {
-			mapping->a_ops->readpage(filp, page);
+			ret = mapping->a_ops->readpage(filp, page);
+			/* 
+			 * If readpage fails, don't proceed with further
+			 * readpage
+			 * */
+			if (ret < 0)
+				alloc = 0;

Before, this the page_cache_release was not happening for the 
rest of the pages.

I will send it in separate patch if this is fine.

> Thanks,
> Fengguang
>
> > Signed-off-by: Raghavendra D Prabhu <rprabhu@xxxxxxxxxxx>
> > ---
> >  mm/readahead.c | 12 +++++++-----
> >  1 file changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/readahead.c b/mm/readahead.c
> > index ea8f8fa..461fcc0 100644
> > --- a/mm/readahead.c
> > +++ b/mm/readahead.c
> > @@ -113,7 +113,7 @@ static int read_pages(struct address_space *mapping, struct file *filp,
> >  {
> >  	struct blk_plug plug;
> >  	unsigned page_idx;
> > -	int ret;
> > +	int ret = 0;
> >
> >  	blk_start_plug(&plug);
> >
> > @@ -129,11 +129,12 @@ static int read_pages(struct address_space *mapping, struct file *filp,
> >  		list_del(&page->lru);
> >  		if (!add_to_page_cache_lru(page, mapping,
> >  					page->index, GFP_KERNEL)) {
> > -			mapping->a_ops->readpage(filp, page);
> > +			ret = mapping->a_ops->readpage(filp, page);
> > +			if (ret < 0)
> > +				break;
> >  		}
> >  		page_cache_release(page);
> >  	}
> > -	ret = 0;
> >
> >  out:
> >  	blk_finish_plug(&plug);
> > @@ -160,6 +161,7 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
> >  	LIST_HEAD(page_pool);
> >  	int page_idx;
> >  	int ret = 0;
> > +	int ret_read = 0;
> >  	loff_t isize = i_size_read(inode);
> >
> >  	if (isize == 0)
> > @@ -198,10 +200,10 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
> >  	 * will then handle the error.
> >  	 */
> >  	if (ret)
> > -		read_pages(mapping, filp, &page_pool, ret);
> > +		ret_read = read_pages(mapping, filp, &page_pool, ret);
> >  	BUG_ON(!list_empty(&page_pool));
> >  out:
> > -	return ret;
> > +	return (ret_read < 0 ? ret_read : ret);
> >  }
> >
> >  /*
> > --
> > 1.7.12.1








Regards,
--
Raghavendra Prabhu
GPG Id : 0xD72BE977
Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977
www: wnohang.net

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