Re: [PATCH v2] Btrfs: add readahead for send_write

[Liu Bo <bo.li.liu@oracle.com>]

On Mon, Mar 03, 2014 at 03:25:28PM +0100, David Sterba wrote:
> On Mon, Mar 03, 2014 at 05:24:43PM +0800, Liu Bo wrote:
> > --- a/fs/btrfs/send.c
> > +++ b/fs/btrfs/send.c
> > @@ -3972,6 +3972,7 @@ static ssize_t fill_read_buf(struct send_ctx *sctx, u64 offset, u32 len)
> >  	pgoff_t last_index;
> >  	unsigned pg_offset = offset & ~PAGE_CACHE_MASK;
> >  	ssize_t ret = 0;
> > +	struct file_ra_state *ra = NULL;
> >  
> >  	key.objectid = sctx->cur_ino;
> >  	key.type = BTRFS_INODE_ITEM_KEY;
> > @@ -3991,6 +3992,17 @@ static ssize_t fill_read_buf(struct send_ctx *sctx, u64 offset, u32 len)
> >  		goto out;
> >  
> >  	last_index = (offset + len - 1) >> PAGE_CACHE_SHIFT;
> > +
> > +	/* initial readahead */
> > +	ra = kzalloc(sizeof(*ra), GFP_NOFS);
> > +	if (!ra) {
> > +		ret = -ENOMEM;
> 
> This should not be a hard failure, it can continue without RA for this
> buffer. Besides, the RA buffer can be allocated at the beginning of send
> operation and pointer stored in the send context.

Good point, I think we can fold this into 'struct send_ctx', do you agree?

Thanks,
-liubo