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Tue, 18 Feb 2020 22:33:21 +0000 (UTC) Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate24.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Tue, 18 Feb 2020 14:32:09 -0800 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Tue, 18 Feb 2020 14:33:20 -0800 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Tue, 18 Feb 2020 14:33:20 -0800 Received: from [10.110.48.28] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 18 Feb 2020 22:33:19 +0000 Subject: Re: [PATCH v6 04/19] mm: Rearrange readahead loop To: Matthew Wilcox , CC: , , , , , , , , References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-5-willy@infradead.org> X-Nvconfidentiality: public From: John Hubbard Message-ID: <6ecedc28-a999-8673-e4b1-349b0c23fdfd@nvidia.com> Date: Tue, 18 Feb 2020 14:33:19 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200217184613.19668-5-willy@infradead.org> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1582065129; bh=yWG75TuvaIkixcYjAReAuF+49IUj/8WtcUdupEFzEyw=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=klykhDzbfDnFoiAzHG0F/sl3+zuD/yu0U05wkkG5YL25K0mXMn/SZDKS/OPYoMjVi mBSMyFlXKKo4UAQQuQv/lsdIWAvE7WxiS+oOmcGMSJDykk7YuHI6JFzdcykchFj71k zIa5A9cfCBqyTcR6zGjigkGmcGSCKI7dxvmn+IuKHqErApkB59r3L/Gj+RxcTKKVSI +btrOqRw+4ZZVhqAz1RhfcawzguTRlv7l99v2wGxH6VlakfW2nQLeICs16ez9TeiWQ ZpdA450G/HarSR+IiezZDL9QVYoCyXag0rX4h00yKEt9Soza8Wdn/b85Sc2AMZZmq3 fR1BnLTnbzkPg== 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: On 2/17/20 10:45 AM, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" > > Move the declaration of 'page' to inside the loop and move the 'kick > off a fresh batch' code to the end of the function for easier use in > subsequent patches. > > Signed-off-by: Matthew Wilcox (Oracle) > --- > mm/readahead.c | 21 +++++++++++++-------- > 1 file changed, 13 insertions(+), 8 deletions(-) > > diff --git a/mm/readahead.c b/mm/readahead.c > index 15329309231f..3eca59c43a45 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -154,7 +154,6 @@ void __do_page_cache_readahead(struct address_space *mapping, > unsigned long lookahead_size) > { > struct inode *inode = mapping->host; > - struct page *page; > unsigned long end_index; /* The last page we want to read */ > LIST_HEAD(page_pool); > int page_idx; > @@ -175,6 +174,7 @@ void __do_page_cache_readahead(struct address_space *mapping, > * Preallocate as many pages as we will need. > */ > for (page_idx = 0; page_idx < nr_to_read; page_idx++) { > + struct page *page; > pgoff_t page_offset = offset + page_idx; > > if (page_offset > end_index) > @@ -183,14 +183,14 @@ void __do_page_cache_readahead(struct address_space *mapping, > page = xa_load(&mapping->i_pages, page_offset); > if (page && !xa_is_value(page)) { > /* > - * Page already present? Kick off the current batch of > - * contiguous pages before continuing with the next > - * batch. > + * Page already present? Kick off the current batch > + * of contiguous pages before continuing with the > + * next batch. This page may be the one we would > + * have intended to mark as Readahead, but we don't > + * have a stable reference to this page, and it's > + * not worth getting one just for that. > */ > - if (readahead_count(&rac)) > - read_pages(&rac, &page_pool, gfp_mask); > - rac._nr_pages = 0; > - continue; A fine point: you'll get better readability and a less complex function by factoring that into a static subroutine, instead of jumping around with goto's. (This clearly wants to be a subroutine, and in fact you've effectively created one inside this function, at the "read:" label. Either way, though... > + goto read; > } > > page = __page_cache_alloc(gfp_mask); > @@ -201,6 +201,11 @@ void __do_page_cache_readahead(struct address_space *mapping, > if (page_idx == nr_to_read - lookahead_size) > SetPageReadahead(page); > rac._nr_pages++; > + continue; > +read: > + if (readahead_count(&rac)) > + read_pages(&rac, &page_pool, gfp_mask); > + rac._nr_pages = 0; > } > > /* > ...no errors spotted, I'm confident that this patch is correct, Reviewed-by: John Hubbard thanks, -- John Hubbard NVIDIA