linux-kernel - Re: [PATCH 5/8] readahead: add /debug/readahead/stats

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Date:	Tue, 29 Nov 2011 20:29:51 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Jens Axboe <jens.axboe@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 5/8] readahead: add /debug/readahead/stats

>  int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
>  		pgoff_t offset, unsigned long nr_to_read)
>  {
> +	struct file_ra_state fadvice_ra = {
> +		.pattern	= RA_PATTERN_FADVISE,
> +	};
>  	int ret = 0;
>  
>  	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
> @@ -222,8 +397,9 @@ int force_page_cache_readahead(struct ad
>  
>  		if (this_chunk > nr_to_read)
>  			this_chunk = nr_to_read;
> -		err = __do_page_cache_readahead(mapping, filp,
> -						offset, this_chunk, 0);
> +		fadvice_ra.start = offset;
> +		fadvice_ra.size = this_chunk;
> +		err = ra_submit(&fadvice_ra, mapping, filp, offset, nr_to_read);
>  		if (err < 0) {
>  			ret = err;
>  			break;

It looks that we can safely use filp->f_ra:

@@ -214,6 +386,7 @@ int force_page_cache_readahead(struct ad
        if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
                return -EINVAL;

+       filp->f_ra.pattern = RA_PATTERN_FADVISE;
        nr_to_read = max_sane_readahead(nr_to_read);
        while (nr_to_read) {
                int err;
@@ -222,8 +395,9 @@ int force_page_cache_readahead(struct ad
               
                if (this_chunk > nr_to_read)
                        this_chunk = nr_to_read;
-               err = __do_page_cache_readahead(mapping, filp,
-                                               offset, this_chunk, 0);
+               filp->f_ra.start = offset;
+               filp->f_ra.size = this_chunk;
+               err = ra_submit(&filp->f_ra, mapping, filp, offset, nr_to_read);
                if (err < 0) {
                        ret = err;
                        break;

But still, it adds one more function call to the fadvise path.

Thanks,
Fengguang
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