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authorNick Piggin <npiggin@suse.de>2008-04-28 05:13:00 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-28 11:58:23 -0400
commit7e675137a8e1a4d45822746456dd389b65745bf6 (patch)
tree5df01d23ea1b6b212d18f2136ff82913fcbe7718 /include/linux/mm.h
parentb379d790197cdf8a95fb67507d75a24ac0a1678d (diff)
mm: introduce pte_special pte bit
s390 for one, cannot implement VM_MIXEDMAP with pfn_valid, due to their memory model (which is more dynamic than most). Instead, they had proposed to implement it with an additional path through vm_normal_page(), using a bit in the pte to determine whether or not the page should be refcounted: vm_normal_page() { ... if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) { if (vma->vm_flags & VM_MIXEDMAP) { #ifdef s390 if (!mixedmap_refcount_pte(pte)) return NULL; #else if (!pfn_valid(pfn)) return NULL; #endif goto out; } ... } This is fine, however if we are allowed to use a bit in the pte to determine refcountedness, we can use that to _completely_ replace all the vma based schemes. So instead of adding more cases to the already complex vma-based scheme, we can have a clearly seperate and simple pte-based scheme (and get slightly better code generation in the process): vm_normal_page() { #ifdef s390 if (!mixedmap_refcount_pte(pte)) return NULL; return pte_page(pte); #else ... #endif } And finally, we may rather make this concept usable by any architecture rather than making it s390 only, so implement a new type of pte state for this. Unfortunately the old vma based code must stay, because some architectures may not be able to spare pte bits. This makes vm_normal_page a little bit more ugly than we would like, but the 2 cases are clearly seperate. So introduce a pte_special pte state, and use it in mm/memory.c. It is currently a noop for all architectures, so this doesn't actually result in any compiled code changes to mm/memory.o. BTW: I haven't put vm_normal_page() into arch code as-per an earlier suggestion. The reason is that, regardless of where vm_normal_page is actually implemented, the *abstraction* is still exactly the same. Also, while it depends on whether the architecture has pte_special or not, that is the only two possible cases, and it really isn't an arch specific function -- the role of the arch code should be to provide primitive functions and accessors with which to build the core code; pte_special does that. We do not want architectures to know or care about vm_normal_page itself, and we definitely don't want them being able to invent something new there out of sight of mm/ code. If we made vm_normal_page an arch function, then we have to make vm_insert_mixed (next patch) an arch function too. So I don't think moving it to arch code fundamentally improves any abstractions, while it does practically make the code more difficult to follow, for both mm and arch developers, and easier to misuse. [akpm@linux-foundation.org: build fix] Signed-off-by: Nick Piggin <npiggin@suse.de> Acked-by: Carsten Otte <cotte@de.ibm.com> Cc: Jared Hulbert <jaredeh@gmail.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/mm.h')
-rw-r--r--include/linux/mm.h4
1 files changed, 3 insertions, 1 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c657ea0bd6aa..ba86ddaa2bb8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -721,7 +721,9 @@ struct zap_details {
721 unsigned long truncate_count; /* Compare vm_truncate_count */ 721 unsigned long truncate_count; /* Compare vm_truncate_count */
722}; 722};
723 723
724struct page *vm_normal_page(struct vm_area_struct *, unsigned long, pte_t); 724struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
725 pte_t pte);
726
725unsigned long zap_page_range(struct vm_area_struct *vma, unsigned long address, 727unsigned long zap_page_range(struct vm_area_struct *vma, unsigned long address,
726 unsigned long size, struct zap_details *); 728 unsigned long size, struct zap_details *);
727unsigned long unmap_vmas(struct mmu_gather **tlb, 729unsigned long unmap_vmas(struct mmu_gather **tlb,