Messages in this thread | | | Date | Thu, 10 Nov 2005 16:00:10 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 01/15] mm: poison struct page for ptlock |
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* Hugh Dickins <hugh@veritas.com> wrote:
> On Thu, 10 Nov 2005, Andrew Morton wrote: > > Hugh Dickins <hugh@veritas.com> wrote: > > > On Thu, 10 Nov 2005, Ingo Molnar wrote: > > > > > > > > yuck. What is the real problem btw? AFAICS there's enough space for a > > > > 2-word spinlock in struct page for pagetables. > > > > > > Yes. There is no real problem. But my patch offends good taste. > > > > Isn't it going to overrun page.lru with CONFIG_DEBUG_SPINLOCK? > > No. There is just one case where it would, > so in that case split ptlock is disabled by mm/Kconfig's > # PA-RISC 7xxx's debug spinlock_t is too large for 32-bit struct page. > > default "4096" if PARISC && DEBUG_SPINLOCK && !PA20 > > Of course, someone may extend spinlock debugging info tomorrow; but > when they do, presumably they'll try it out, and hit the BUILD_BUG_ON. > They'll then probably want to extend the suppression in mm/Kconfig.
why not do the union thing so that struct page grows automatically as new fields are added? It is quite bad design to introduce a hard limit like that. The only sizing concern is to make sure that the common .configs dont increase the size of struct page, but otherwise why not allow a larger struct page - it's for debugging only.
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