From mboxrd@z Thu Jan 1 00:00:00 1970 From: mina86@mina86.com (Michal Nazarewicz) Date: Fri, 01 Apr 2011 00:51:32 +0200 Subject: [PATCH 04/12] mm: alloc_contig_freed_pages() added In-Reply-To: <1301610411.30870.29.camel@nimitz> References: <1301577368-16095-1-git-send-email-m.szyprowski@samsung.com> <1301577368-16095-5-git-send-email-m.szyprowski@samsung.com> <1301587083.31087.1032.camel@nimitz> <1301606078.31087.1275.camel@nimitz> <1301610411.30870.29.camel@nimitz> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, 01 Apr 2011 00:26:51 +0200, Dave Hansen wrote: > On Fri, 2011-04-01 at 00:18 +0200, Michal Nazarewicz wrote: >> On Thu, 31 Mar 2011 23:14:38 +0200, Dave Hansen wrote: >> > We BUG_ON() in bootmem. Basically if we try to allocate an early-boot >> > structure and fail, we're screwed. We can't keep running without an >> > inode hash, or a mem_map[]. >> > >> > This looks like it's going to at least get partially used in drivers, >> at >> > least from the examples. Are these kinds of things that, if the >> driver >> > fails to load, that the system is useless and hosed? Or, is it >> > something where we might limp along to figure out what went wrong >> before >> > we reboot? >> >> Bug in the above place does not mean that we could not allocate >> memory. It means caller is broken. > > Could you explain that a bit? > > Is this a case where a device is mapped to a very *specific* range of > physical memory and no where else? What are the reasons for not marking > it off limits at boot? I also saw some bits of isolation and migration > in those patches. Can't the migration fail? The function is called from alloc_contig_range() (see patch 05/12) which makes sure that the PFN is valid. Situation where there is not enough space is caught earlier in alloc_contig_range(). alloc_contig_freed_pages() must be given a valid PFN range such that all the pages in that range are free (as in are within the region tracked by page allocator) and of MIGRATETYPE_ISOLATE so that page allocator won't touch them. That's why invalid PFN is a bug in the caller and not an exception that has to be handled. Also, the function is not called during boot time. It is called while system is already running. -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Michal "mina86" Nazarewicz (o o) ooo +----------ooO--(_)--Ooo--