Re: [PATCH 3/4] readahead: factor out duplicated code

[Oleg Nesterov]

Steven Pratt wrote:
>
> >+static int make_ahead_window(struct address_space *mapping, struct file *filp,
> >+		struct file_ra_state *ra, int force)
> >+{
> >+	int block, ret;
> >+
> >+	block = force || (ra->prev_page >= ra->ahead_start);
> >+	ret = blockable_page_cache_readahead(mapping, filp,
> >+			ra->ahead_start, ra->ahead_size, ra, block);
> >+
> >+	if (!ret && !force) {
> >
> This really needs to be
>
>     if (!ret && !block) {
>

Current code:

	block = offset + newsize-1 >= ra->ahead_start;
	if (!blockable_page_cache_readahead(..., block) {
		ra->ahead_start = 0;
		ra->ahead_size = 0;
	}

Patched code:
	make_ahead_window(..., 0); // force == 0

So i think the patch is correct.

> otherwise we can have an aheadwindow which was never populated which
> will cause slow reads which we want to avoid in all cases.

may be, but this patch tries not to change the current behavior.

Oleg.
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