From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sun, 4 Apr 2004 01:27:17 +0200 From: Andrea Arcangeli Subject: Re: [RFC][PATCH 1/3] radix priority search tree - objrmap complexity fix Message-ID: <20040403232717.GO2307@dualathlon.random> References: <20040402001535.GG18585@dualathlon.random> <20040402011627.GK18585@dualathlon.random> <20040401173649.22f734cd.akpm@osdl.org> <20040402020022.GN18585@dualathlon.random> <20040402104334.A871@infradead.org> <20040402164634.GF21341@dualathlon.random> <20040403174043.GK2307@dualathlon.random> <20040403120227.398268aa.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040403120227.398268aa.akpm@osdl.org> Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: hch@infradead.org, hugh@veritas.com, vrajesh@umich.edu, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Sat, Apr 03, 2004 at 12:02:27PM -0800, Andrew Morton wrote: > It might be better to switch over to address masking in get_user_pages() > and just dump all the compound page logic. I don't immediately see how the I'm all for it, this is how the 2.4 get_user_pages deals with bigpages too, I've never enjoyed the compound thing. > get_user_pages() caller can subsequently do put_page() against the correct > pageframe, but I assume you worked that out? see this patch: http://www.us.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.23aa2/9910_shm-largepage-18.gz it's a two liner fix in follow_page: @@ -439,6 +457,8 @@ static struct page * follow_page(struct pmd = pmd_offset(pgd, address); if (pmd_none(*pmd)) goto out; + if (pmd_bigpage(*pmd)) + return __pmd_page(*pmd) + (address & BIGPAGE_MASK) / PAGE_SIZE; the BIGPAGE_MASK will never expose anything but the page->private to the get_user_pages code, and handle_mm_fault takes care of doing the page faults properly using larepages and pmds if the vma is marked VM_BIGPAGE. rawio on largepages has been a must-have feature (especially on >=32G) for more than one year, definitely no need of compound slowdown for that. Still I would like to understand what's wrong in Christoph's ppc machine before dumping the whole compound thing. -- 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: aart@kvack.org