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a=rsa-sha256; c=relaxed/relaxed; d=pankajraghav.com; s=MBO0001; t=1718357169; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=wKdlyvSF7pCAKamuIrCSdc2r5zUKZ+TWhLzB5NWF7sE=; b=ZZR1KZsBATXt8TUkNrnhy8NPhWZ9HUbnl97kMLnlKWta4bA6DEM9xTjmRsLAywUnIo1+uJ WmIdOXXLqbhBqN4yKShp/3Jh4Vhh9ndbSK8s2AuJ/UjPiX17lfrdZQLDjQFp7B247DGzAT FJeiStNCfo/wUbsWMrDsISWpyYt9wM+6aWeE+RoOaEO254zxRcT3NKpjM9Kr+R5TCZvy1p 3WfAK7OyQnxP+oo6W/CZ6OFyullms/6FRAX5KX+IeEFQMc5iEEyd/1GPX36S+ja3om8hH7 UsonYuuQWcaKM09pD9TVtUdBShHkBQRK51vqaAk5F3JUfHvoRXI76i61GMpWmQ== Date: Fri, 14 Jun 2024 09:26:02 +0000 From: "Pankaj Raghav (Samsung)" To: Matthew Wilcox Cc: david@fromorbit.com, djwong@kernel.org, chandan.babu@oracle.com, brauner@kernel.org, akpm@linux-foundation.org, mcgrof@kernel.org, linux-mm@kvack.org, hare@suse.de, linux-kernel@vger.kernel.org, yang@os.amperecomputing.com, Zi Yan , linux-xfs@vger.kernel.org, p.raghav@samsung.com, linux-fsdevel@vger.kernel.org, hch@lst.de, gost.dev@samsung.com, cl@os.amperecomputing.com, john.g.garry@oracle.com Subject: Re: [PATCH v7 04/11] readahead: allocate folios with mapping_min_order in readahead Message-ID: <20240614092602.jc5qeoxy24xj6kl7@quentin> References: <20240607145902.1137853-1-kernel@pankajraghav.com> <20240607145902.1137853-5-kernel@pankajraghav.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 7wqifsesgpwzoa49u8b9rgnducddocsw X-Rspamd-Queue-Id: 0BBEFC000D X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1718357173-736630 X-HE-Meta: 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 PV2ciBVV ORsksUtuIhRqFUTRo3NhtEZgRZZ0qgxJyjniXasKcW1KwXQDVC4T2z75SAxFkCA1si1Jqe9YNaMAAH1wELkLGhDg+bd0wMIf2oesWN1G34jo1qte+RnnE/K62lCeAYdQkwb+a8ds7NtS+6kE+FPOo0w2hRyX4T9SBEHoek69HqZvfUXMnSY/ky0ja+KHjxAmNIuY8PpsALxtkOi4Mg/pEte1Fcvp02L9xNi8NE0lgu4L+LOsWZqtpZXsMxqjr0O4c3qVZ/i3UF1EQcgCBlr+dIQVCYICFnl8aHTc3NSrgN7EwBus= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jun 12, 2024 at 07:50:49PM +0100, Matthew Wilcox wrote: > On Fri, Jun 07, 2024 at 02:58:55PM +0000, Pankaj Raghav (Samsung) wrote: > > @@ -230,7 +247,9 @@ void page_cache_ra_unbounded(struct readahead_control *ractl, > > struct folio *folio = xa_load(&mapping->i_pages, index + i); > > int ret; > > > > + > > Spurious newline Oops. > > > if (folio && !xa_is_value(folio)) { > > + long nr_pages = folio_nr_pages(folio); > > Hm, but we don't have a reference on this folio. So this isn't safe. > That is why I added a check for mapping after read_pages(). You are right, we can make it better. > > @@ -240,12 +259,24 @@ void page_cache_ra_unbounded(struct readahead_control *ractl, > > * not worth getting one just for that. > > */ > > read_pages(ractl); > > - ractl->_index += folio_nr_pages(folio); > > + > > + /* > > + * 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; > > Why not just: > ractl->_index += min_nrpages; Then we will only move min_nrpages even if the folio we found had a bigger order. Hannes patches (first patch) made sure we move the ractl->index by folio_nr_pages instead of 1 and making this change will defeat the purpose because without mapping order set, min_nrpages will be 1. What I could do is the follows: diff --git a/mm/readahead.c b/mm/readahead.c index 389cd802da63..92cf45cdb4d3 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -249,7 +249,7 @@ void page_cache_ra_unbounded(struct readahead_control *ractl, if (folio && !xa_is_value(folio)) { - long nr_pages = folio_nr_pages(folio); + long nr_pages; /* * Page already present? Kick off the current batch * of contiguous pages before continuing with the @@ -266,10 +266,8 @@ void page_cache_ra_unbounded(struct readahead_control *ractl, * alignment constraint in the page cache. * */ - if (mapping != folio->mapping) - nr_pages = min_nrpages; + nr_pages = max(folio_nr_pages(folio), (long)min_nrpages); - VM_BUG_ON_FOLIO(nr_pages < min_nrpages, folio); ractl->_index += nr_pages; i = ractl->_index + ractl->_nr_pages - index; continue; Now we will still move respecting the min order constraint but if we had a bigger folio and we do have a reference, then we move folio_nr_pages. > > like you do below? Below we add a folio of min_order, so if that fails for some reason, we can unconditionally move min_nrpages.