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Date: Tue, 15 Apr 2008 21:43:59 +0200 From: Johannes Weiner <hannes@...urebad.de> To: "Yinghai Lu" <yhlu.kernel@...il.com> 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() Hi, "Yinghai Lu" <yhlu.kernel@...il.com> writes: > 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? Yep, already looked at them. My patches were initially against Linus' tree which does not allow bootmem to act across node boundaries yet. Regarding node-crossing, what do you think about my idea in http://lkml.org/lkml/2008/4/15/139? That way we could preserve the core functions and keep them clean. The design could of course be applied to the other node-crossing functions too. Hannes -- 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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