From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Whitcroft Subject: Re: [PATCH 2/2] hugetlb reservations: fix hugetlb MAP_PRIVATE reservations across vma splits Date: Mon, 23 Jun 2008 10:53:10 +0100 Message-ID: <20080623095310.GH29804@shadowen.org> References: <1213989474-5586-1-git-send-email-apw@shadowen.org> <1213989474-5586-3-git-send-email-apw@shadowen.org> <20080623080048.GJ21597@csn.ul.ie> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20080623080048.GJ21597-wPRd99KPJ+uzQB+pC5nmwQ@public.gmane.org> Sender: kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Mel Gorman Cc: Jon Tollefson , Andrew Morton , Nick Piggin , Nishanth Aravamudan , Adam Litke , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-testers-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org On Mon, Jun 23, 2008 at 09:00:48AM +0100, Mel Gorman wrote: > Typical. I spotted this after I pushed send..... > > > > > > @@ -266,14 +326,19 @@ static void decrement_hugepage_resv_vma(struct hstate *h, > > * private mappings. > > */ > > if (is_vma_resv_set(vma, HPAGE_RESV_OWNER)) { > > - unsigned long flags, reserve; > > + unsigned long idx = vma_pagecache_offset(h, > > + vma, address); > > + struct resv_map *reservations = vma_resv_map(vma); > > + > > h->resv_huge_pages--; > > - flags = (unsigned long)vma->vm_private_data & > > - HPAGE_RESV_MASK; > > - reserve = (unsigned long)vma->vm_private_data - 1; > > - vma->vm_private_data = (void *)(reserve | flags); > > + > > + /* Mark this page used in the map. */ > > + if (region_chg(&reservations->regions, idx, idx + 1) < 0) > > + return -1; > > + region_add(&reservations->regions, idx, idx + 1); > > } > > decrement_hugepage_resv_vma() is called with hugetlb_lock held and region_chg > calls kmalloc(GFP_KERNEL). Hence it's possible we would sleep with that > spinlock held which is a bit uncool. The allocation needs to happen outside > the lock. Right? Yes, good spot. Luckily this pair of calls can be separated, as the first is a prepare and the second a commit. So I can trivially pull the allocation outside the lock. Had a quick go at this and it looks like I can move both out of the lock to a much more logical spot and clean the patch up significantly. Will fold in your other comments and post up a V2 once it has been tested. Thanks. -apw