On Wed 29-11-17 13:41:59, Andrew Morton wrote: > On Wed, 29 Nov 2017 17:04:46 +0100 Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > On Mon 27-11-17 12:33:41, Michal Hocko wrote: > > > On Mon 27-11-17 19:09:24, JianKang Chen wrote: > > > > From: Jiankang Chen <chenjiankang1@xxxxxxxxxx> > > > > > > > > __get_free_pages will return an virtual address, > > > > but it is not just 32-bit address, for example a 64-bit system. > > > > And this comment really confuse new bigenner of mm. > > > > > > s@bigenner@beginner@ > > > > > > Anyway, do we really need a bug on for this? Has this actually caught > > > any wrong usage? VM_BUG_ON tends to be enabled these days AFAIK and > > > panicking the kernel seems like an over-reaction. If there is a real > > > risk then why don't we simply mask __GFP_HIGHMEM off when calling > > > alloc_pages? > > > > I meant this > > --- > > >From 000bb422fe07adbfa8cd8ed953b18f48647a45d6 Mon Sep 17 00:00:00 2001 > > From: Michal Hocko <mhocko@xxxxxxxx> > > Date: Wed, 29 Nov 2017 17:02:33 +0100 > > Subject: [PATCH] mm: drop VM_BUG_ON from __get_free_pages > > > > There is no real reason to blow up just because the caller doesn't know > > that __get_free_pages cannot return highmem pages. Simply fix that up > > silently. Even if we have some confused users such a fixup will not be > > harmful. > > mm... So we have a caller which hopes to be getting highmem pages but > isn't. Caller then proceeds to pointlessly kmap the page and wonders > why it isn't getting as much memory as it would like on 32-bit systems, > etc. How he can kmap the page when he gets a _virtual_ address? > I do think we should help ferret out such bogosity. A WARN_ON_ONCE > would suffice. This function has always been about lowmem pages. I seriously doubt we have anybody confused and asking for a highmem page in the kernel. I haven't checked that but it would already blow up as VM_BUG_ON tends to be enabled on many setups. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
