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Date: Tue, 27 Feb 2024 13:42:51 +0100
From: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, 
	linux-kernel@vger.kernel.org, david@fromorbit.com, chandan.babu@oracle.com, 
	akpm@linux-foundation.org, mcgrof@kernel.org, ziy@nvidia.com, hare@suse.de, 
	djwong@kernel.org, gost.dev@samsung.com, linux-mm@kvack.org, 
	Pankaj Raghav <p.raghav@samsung.com>
Subject: Re: [PATCH 05/13] readahead: set file_ra_state->ra_pages to be at
 least mapping_min_order
Message-ID: <ea3lppsqtgc6u7o4boj4j72mq5xp74o3csegvd5inkhll4nbpb@d6qcj4vem5ao>
References: <20240226094936.2677493-1-kernel@pankajraghav.com>
 <20240226094936.2677493-6-kernel@pankajraghav.com>
 <Zdyk4ErGQHc1q-1W@casper.infradead.org>
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On Mon, Feb 26, 2024 at 02:49:04PM +0000, Matthew Wilcox wrote:
> On Mon, Feb 26, 2024 at 10:49:28AM +0100, Pankaj Raghav (Samsung) wrote:
> > From: Luis Chamberlain <mcgrof@kernel.org>
> > 
> > Set the file_ra_state->ra_pages in file_ra_state_init() to be at least
> > mapping_min_order of pages if the bdi->ra_pages is less than that.
> 
> Don't we rather want to round up to a multiple of mapping_min_nrpages?

Hmm. That will definitely be more explicit. We might be doing
multiple of min_nrpages now anyway, going beyond the ra_pages(if it 
is not a multiple of min_nrpages).

I will do this instead:

diff --git a/mm/readahead.c b/mm/readahead.c
index 73aef3f080ba..4e3a6f763f5c 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -138,11 +138,8 @@
 void
 file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
 {
-       unsigned int min_nrpages = mapping_min_folio_nrpages(mapping);
-
-       ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
-       if (ra->ra_pages < min_nrpages)
-               ra->ra_pages = min_nrpages;
+       ra->ra_pages = round_up(inode_to_bdi(mapping->host)->ra_pages,
+                               mapping_min_folio_nrpages(mapping));
        ra->prev_pos = -1;
 }

> 
> >  file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping)
> >  {
> > +	unsigned int min_nrpages = mapping_min_folio_nrpages(mapping);
> > +
> >  	ra->ra_pages = inode_to_bdi(mapping->host)->ra_pages;
> > +	if (ra->ra_pages < min_nrpages)
> > +		ra->ra_pages = min_nrpages;
> >  	ra->prev_pos = -1;