From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f72.google.com (mail-lf0-f72.google.com [209.85.215.72]) by kanga.kvack.org (Postfix) with ESMTP id 703256B0387 for ; Mon, 13 Feb 2017 10:33:46 -0500 (EST) Received: by mail-lf0-f72.google.com with SMTP id v186so44488752lfa.2 for ; Mon, 13 Feb 2017 07:33:46 -0800 (PST) Received: from mail-wr0-x244.google.com (mail-wr0-x244.google.com. [2a00:1450:400c:c0c::244]) by mx.google.com with ESMTPS id f78si5961917wmd.44.2017.02.13.07.33.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 13 Feb 2017 07:33:45 -0800 (PST) Received: by mail-wr0-x244.google.com with SMTP id 89so24664300wrr.1 for ; Mon, 13 Feb 2017 07:33:45 -0800 (PST) Date: Mon, 13 Feb 2017 18:33:42 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCHv6 08/37] filemap: handle huge pages in do_generic_file_read() Message-ID: <20170213153342.GE20394@node.shutemov.name> References: <20170126115819.58875-1-kirill.shutemov@linux.intel.com> <20170126115819.58875-9-kirill.shutemov@linux.intel.com> <20170209215505.GW2267@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170209215505.GW2267@bombadil.infradead.org> Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: "Kirill A. Shutemov" , Theodore Ts'o , Andreas Dilger , Jan Kara , Andrew Morton , Alexander Viro , Hugh Dickins , Andrea Arcangeli , Dave Hansen , Vlastimil Babka , Ross Zwisler , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org On Thu, Feb 09, 2017 at 01:55:05PM -0800, Matthew Wilcox wrote: > On Thu, Jan 26, 2017 at 02:57:50PM +0300, Kirill A. Shutemov wrote: > > +++ b/mm/filemap.c > > @@ -1886,6 +1886,7 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos, > > if (unlikely(page == NULL)) > > goto no_cached_page; > > } > > + page = compound_head(page); > > We got this page from find_get_page(), which gets it from > pagecache_get_page(), which gets it from find_get_entry() ... which > (unless I'm lost in your patch series) returns the head page. So this > line is redundant, right? No. pagecache_get_page() returns subpage. See description of the first patch. > But then down in filemap_fault, we have: > > VM_BUG_ON_PAGE(page->index != offset, page); > > ... again, maybe I'm lost somewhere in your patch series, but I don't see > anywhere you remove that line (or modify it). This should be fine as find_get_page() returns subpage. > So are you not testing > with VM debugging enabled, or are you not doing a test which includes > mapping a file with huge pages, reading from it (to get the page in cache), > then faulting on an address that is not in the first 4kB of that 2MB? > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org