From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id A12FA6B0387 for ; Thu, 9 Feb 2017 16:57:15 -0500 (EST) Received: by mail-pf0-f198.google.com with SMTP id c73so23267877pfb.7 for ; Thu, 09 Feb 2017 13:57:15 -0800 (PST) Received: from bombadil.infradead.org (bombadil.infradead.org. [65.50.211.133]) by mx.google.com with ESMTPS id p66si11234653pga.87.2017.02.09.13.57.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 09 Feb 2017 13:57:14 -0800 (PST) Date: Thu, 9 Feb 2017 13:55:05 -0800 From: Matthew Wilcox Subject: Re: [PATCHv6 08/37] filemap: handle huge pages in do_generic_file_read() Message-ID: <20170209215505.GW2267@bombadil.infradead.org> References: <20170126115819.58875-1-kirill.shutemov@linux.intel.com> <20170126115819.58875-9-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170126115819.58875-9-kirill.shutemov@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: 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, 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? 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). 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