Re: [patch 2/2] bootmem: Node-setup agnostic free_bootmem()

[Yinghai Lu]

On Tue, Apr 15, 2008 at 4:51 AM, Johannes Weiner <hannes@xxxxxxxxxxxx> wrote:
> Hi,
>
>
>
>  Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes:
>
>  > On Tue, 15 Apr 2008 00:28:34 -0700 "Yinghai Lu" <yhlu.kernel@xxxxxxxxx> wrote:
>  >
>  >> On Tue, Apr 15, 2008 at 12:15 AM, Andrew Morton
>  >> <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>  >> >
>  >> > On Tue, 15 Apr 2008 00:04:03 -0700 "Yinghai Lu" <yhlu.kernel@xxxxxxxxx> wrote:
>  >> >
>  >> >  > On Mon, Apr 14, 2008 at 11:23 PM, Andrew Morton
>  >> >  > <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>  >> >  > >
>  >> >  > > On Sun, 13 Apr 2008 18:56:57 +0200 Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
>  >> >  > >
>  >> >  > >  > Johannes Weiner <hannes@xxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
>  >> >  > >  >
>  >> >  > >  > 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@xxxxxxxxxxxx> wrote:
>  >> >
>  >> >  > Hi,
>  >> >  >
>  >> >  > "Yinghai Lu" <yhlu.kernel@xxxxxxxxx> writes:
>  >> >  >
>  >> >  > > On Sat, Apr 12, 2008 at 3:33 PM, Johannes Weiner <hannes@xxxxxxxxxxxx> 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
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