Re: [PATCH 20/33] readahead: initial method - expected read size

Wu Fengguang
2006-05-27T06:38:20Z

On Fri, May 26, 2006 at 10:29:34AM -0700, Andrew Morton wrote:
> Wu Fengguang <wfg@mail.ustc.edu.cn> wrote:
> >
> > backing_dev_info.ra_expect_bytes is dynamicly updated to be the expected
> > read pages on start-of-file. It allows the initial readahead to be more
> > aggressive and hence efficient.
> >
> >
> > +void fastcall readahead_close(struct file *file)
>
> eww, fastcall.

Hehe, it's a tiny function, and calls no further sub-routines
except debugging ones. Still not necessary?

> > +{
> > + struct inode *inode = file->f_dentry->d_inode;
> > + struct address_space *mapping = inode->i_mapping;
> > + struct backing_dev_info *bdi = mapping->backing_dev_info;
> > + unsigned long pos = file->f_pos;
>
> f_pos is loff_t.

Just meant to be a little more compact ;)

+ unsigned long pos = file->f_pos;
+ unsigned long pgrahit = file->f_ra.cache_hits;
+ unsigned long pgaccess = 1 + pos / PAGE_CACHE_SIZE;
+ unsigned long pgcached = mapping->nrpages;
+
+ if (!pos) /* pread */
+ return;
+
+ if (pgcached > bdi->ra_pages0) /* excessive reads */
+ return;

Here the f_pos will almost definitely has small values.

+
+ if (pgaccess >= pgcached) {

Fixed by adding a comment to clarify it:

+ unsigned long pos = file->f_pos; /* supposed to be small */