linux-kernel - Re: [PATCH v7 04/11] readahead: allocate folios with mapping_min

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Date: Fri, 21 Jun 2024 12:19:03 +0000
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Hannes Reinecke <hare@...e.de>
Cc: Matthew Wilcox <willy@...radead.org>, david@...morbit.com,
	djwong@...nel.org, chandan.babu@...cle.com, brauner@...nel.org,
	akpm@...ux-foundation.org, mcgrof@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, yang@...amperecomputing.com,
	Zi Yan <zi.yan@...t.com>, linux-xfs@...r.kernel.org,
	p.raghav@...sung.com, linux-fsdevel@...r.kernel.org, hch@....de,
	gost.dev@...sung.com, cl@...amperecomputing.com,
	john.g.garry@...cle.com
Subject: Re: [PATCH v7 04/11] readahead: allocate folios with
 mapping_min_order in readahead

On Tue, Jun 18, 2024 at 08:56:53AM +0200, Hannes Reinecke wrote:
> On 6/17/24 18:39, Pankaj Raghav (Samsung) wrote:
> > On Mon, Jun 17, 2024 at 05:10:15PM +0100, Matthew Wilcox wrote:
> > > On Mon, Jun 17, 2024 at 04:04:20PM +0000, Pankaj Raghav (Samsung) wrote:
> > > > On Mon, Jun 17, 2024 at 01:32:42PM +0100, Matthew Wilcox wrote:
> > > > So the following can still be there from Hannes patch as we have a
> > > > stable reference:
> > > > 
> > > >   		ractl->_workingset |= folio_test_workingset(folio);
> > > > -		ractl->_nr_pages++;
> > > > +		ractl->_nr_pages += folio_nr_pages(folio);
> > > > +		i += folio_nr_pages(folio);
> > > >   	}
> > > 
> > > We _can_, but we just allocated it, so we know what size it is already.
> > Yes.
> > 
> > > I'm starting to feel that Hannes' patch should be combined with this
> > > one.
> > 
> > Fine by me. @Hannes, is that ok with you?
> 
> Sure. I was about to re-send my patchset anyway, so feel free to wrap it in.
Is it ok if I add your Co-developed and Signed-off tag?
This is what I have combining your patch with mine and making willy's
changes:

diff --git a/mm/readahead.c b/mm/readahead.c
index 389cd802da63..f56da953c130 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -247,9 +247,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
                struct folio *folio = xa_load(&mapping->i_pages, index + i);
                int ret;
 
-
                if (folio && !xa_is_value(folio)) {
-                       long nr_pages = folio_nr_pages(folio);
                        /*
                         * Page already present?  Kick off the current batch
                         * of contiguous pages before continuing with the
@@ -259,18 +257,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
                         * not worth getting one just for that.
                         */
                        read_pages(ractl);
-
-                       /*
-                        * Move the ractl->_index by at least min_pages
-                        * if the folio got truncated to respect the
-                        * alignment constraint in the page cache.
-                        *
-                        */
-                       if (mapping != folio->mapping)
-                               nr_pages = min_nrpages;
-
-                       VM_BUG_ON_FOLIO(nr_pages < min_nrpages, folio);
-                       ractl->_index += nr_pages;
+                       ractl->_index += min_nrpages;
                        i = ractl->_index + ractl->_nr_pages - index;
                        continue;
                }
@@ -293,8 +280,8 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
                if (i == mark)
                        folio_set_readahead(folio);
                ractl->_workingset |= folio_test_workingset(folio);
-               ractl->_nr_pages += folio_nr_pages(folio);
-               i += folio_nr_pages(folio);
+               ractl->_nr_pages += min_nrpages;
+               i += min_nrpages;
        }
 
        /*