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Message-ID: <86802c440804151152i1db7bff8n4b64eba8b912d49f@mail.gmail.com> Date: Tue, 15 Apr 2008 11:52:14 -0700 From: "Yinghai Lu" <yhlu.kernel@...il.com> To: "Johannes Weiner" <hannes@...urebad.de> Cc: "Andrew Morton" <akpm@...ux-foundation.org>, "Andi Kleen" <andi@...stfloor.org>, linux-kernel@...r.kernel.org, "Ingo Molnar" <mingo@...e.hu>, "Yasunori Goto" <y-goto@...fujitsu.com>, "KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>, "Christoph Lameter" <clameter@....com> Subject: Re: [patch 2/2] bootmem: Node-setup agnostic free_bootmem() On Tue, Apr 15, 2008 at 4:51 AM, Johannes Weiner <hannes@...urebad.de> wrote: > Hi, > > > > Andrew Morton <akpm@...ux-foundation.org> writes: > > > On Tue, 15 Apr 2008 00:28:34 -0700 "Yinghai Lu" <yhlu.kernel@...il.com> wrote: > > > >> On Tue, Apr 15, 2008 at 12:15 AM, Andrew Morton > >> <akpm@...ux-foundation.org> wrote: > >> > > >> > On Tue, 15 Apr 2008 00:04:03 -0700 "Yinghai Lu" <yhlu.kernel@...il.com> wrote: > >> > > >> > > On Mon, Apr 14, 2008 at 11:23 PM, Andrew Morton > >> > > <akpm@...ux-foundation.org> wrote: > >> > > > > >> > > > On Sun, 13 Apr 2008 18:56:57 +0200 Andi Kleen <andi@...stfloor.org> wrote: > >> > > > > >> > > > > Johannes Weiner <hannes@...urebad.de> writes: > >> > > > > > >> > > > > > Make free_bootmem() look up the node holding the specified address > >> > > > > > range which lets it work transparently on single-node and multi-node > >> > > > > > configurations. > >> > > > > > >> > > > > Acked-by: Andi Kleen <andi@...stfloor.org> > >> > > > > > >> > > > > This is far better than the original change it replaces and which > >> > > > > I also objected to in review. > >> > > > > > >> > > > > >> > > > So... do we think these two patches are sufficiently safe and important for > >> > > > 2.6.25? > >> > > > >> > > the patch is wrong > >> > > > >> > > >> > The last I saw was this: > >> > > >> > > >> > On Sun, 13 Apr 2008 12:57:22 +0200 Johannes Weiner <hannes@...urebad.de> wrote: > >> > > >> > > Hi, > >> > > > >> > > "Yinghai Lu" <yhlu.kernel@...il.com> writes: > >> > > > >> > > > On Sat, Apr 12, 2008 at 3:33 PM, Johannes Weiner <hannes@...urebad.de> wrote: > >> > > > ... > >> > > >> > > > > >> > > > could have chance that bootmem with reserved_early that is crossing > >> > > > the nodes. > >> > > > >> > > Upstream reserve_bootmem_core() would BUG() on a caller trying to cross > >> > > nodes, so I don't see where this chance could come from. > >> > > >> > Is that what you're referring to? > >> > > >> > Was Johannes observation incorrect? If so, why? > >> > >> my patch with free_bootmem will make sure free_bootmem_core only free > >> bootmem in the bdata scope. > >> so free_bootmem can handle the cross_node bootmem that is done by > >> reserve_early ( done in another patch, is dropped by you because took > >> Jonannes). > >> > >> in setup_arch for x86_64 there is one free_bootmem that is used when > >> ramdisk is falled out of ram map. that could be crossed by bootloader > >> and kexec, and kernel or second kernel is memmap=NN@SS to execlue some > >> memory. > >> > >> anyway that is extrem case, but my patch could handle that. > > Has this case ever occured? If this could become real, I have no > objections to implement a way to handle it (why would I?), but until now > you just said that in some time in the future, this could be useful. > > > >> > >> I wonder if any regression caused by my previous patch? maybe on other platform? > >> > > > > Not that I'm aware of. > > It papers over buggy usage of free_bootmem(). If its arguments are > bogus, it will just return again where it BUG()ed out before. The pages > might be never marked free and therefor never reach the buddy allocator. > > > > I restored mm-make-reserve_bootmem-can-crossed-the-nodes.patch. Johannes, > > can you please check 2.6.28-rc8-mm2, see if it looks OK? > > I object to the way it is implemented. If it is really needed, that > should be done properly: > > - remove the double loop over the area on the likely succeeding > path and unroll the reserving on the unlikely path as it was > done before. Better to punish exceptional branches than > the working paths. > - make reserve_bootmem_core be strict with its arguments. If > you want to iterate over the bdata list, you should not just > throw every item at the _core functions and let them work it > out for themselves. The correct parameters should be > calculated in advance and then passed to a strict > _bootmem_core() function that BUG()s on failure. > > But still, Yinghai, you never brought in practical reasons for this > whole thing. You talked about extreme and theoretical cases and I don't > think that this justifies breaking API or pessimizing code at all. free_bootmem(ramdisk_image, ramdisk_size) is sitting in setup_arch of x86_64. or make that panic directly. what i needed is: free_bootmem can free bootmem cross the nodes. on numa alloc_bootmem always return blocks on same nodes. but some via reserve_early and then to bootmem via early_res_to_bootmem could be crossing nodes. BTW, can you look at patches in -mm about make reserve_bootmem cross the nodes? YH -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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