Messages in this thread Patch in this message | | | Date | Wed, 19 Sep 2018 13:51:58 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH 01/11] asm-generic/tlb: Provide a comment |
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On Fri, Sep 14, 2018 at 05:48:57PM +0100, Will Deacon wrote:
> > + * - mmu_gather::fullmm > > + * > > + * A flag set by tlb_gather_mmu() to indicate we're going to free > > + * the entire mm; this allows a number of optimizations. > > + * > > + * XXX list optimizations > > On arm64, we can elide the invalidation altogether because we won't > re-allocate the ASID. We also have an invalidate-by-ASID (mm) instruction, > which we could use if we needed to.
Right, but I was also struggling to put into words the normal fullmm case.
I now ended up with:
--- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -82,7 +82,11 @@ * A flag set by tlb_gather_mmu() to indicate we're going to free * the entire mm; this allows a number of optimizations. * - * XXX list optimizations + * - We can ignore tlb_{start,end}_vma(); because we don't + * care about ranges. Everything will be shot down. + * + * - (RISC) architectures that use ASIDs can cycle to a new ASID + * and delay the invalidation until ASID space runs out. * * - mmu_gather::need_flush_all * Does that about cover things; or do we need more?
> > + * > > + * - mmu_gather::need_flush_all > > + * > > + * A flag that can be set by the arch code if it wants to force > > + * flush the entire TLB irrespective of the range. For instance > > + * x86-PAE needs this when changing top-level entries. > > + * > > + * And requires the architecture to provide and implement tlb_flush(). > > + * > > + * tlb_flush() may, in addition to the above mentioned mmu_gather fields, make > > + * use of: > > + * > > + * - mmu_gather::start / mmu_gather::end > > + * > > + * which (when !need_flush_all; fullmm will have start = end = ~0UL) provides > > + * the range that needs to be flushed to cover the pages to be freed. > > I don't understand the mention of need_flush_all here -- I didn't think it > was used by the core code at all.
The core does indeed not use that flag; but if the architecture set that, the range is still ignored.
Can you suggest clearer wording?
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