Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes: > On Sun, May 23, 2021 at 11:04 PM Aneesh Kumar K.V > <aneesh.kumar@xxxxxxxxxxxxx> wrote: >> >> Add new helper flush_pte_tlb_pwc_range() which invalidates both TLB and >> page walk cache where TLB entries are mapped with page size PAGE_SIZE. > > So I dislike this patch for two reasons: > > (a) naming. > > If the ppc people want to use crazy TLA's that have no meaning outside > of the powerpc community, that's fine. But only in powerpc code. > > "pwc" makes no sense to me, or to anybody else that isn't intimately > involved in low-level powerpc stuff. I assume it's "page walk cache", > but honestly, outside of this area, PWC is mostly used for a specific > type of webcam. > > So there's no way I'd accept this as-is, simply because of that. > flush_pte_tlb_pwc_range() is simply not an acceptable name. You would > have to spell it out, not use an obscure TLA. > > But I think you don't even want to do that, because of How about flush_tlb_and_page_table_cache() ? > > (b) is this even worth it as a public interface? > > Why doesn't the powerpc radix TLB flushing code just always flush the > page table walking cache when the range is larger than a PMD? > > Once you have big flush ranges like that, I don't believe it makes any > sense not to flush the walking cache too. But such a large range invalidate doesn't imply we are freeing page tables. Hence forcing a page table cache flush for large range invalidate can have performance impact. ppc64 don't do a range page table cache invalidate. Hence we will have to flush the full page table cache. > > NOTE! This is particularly true as "flush the walking cache" isn't a > well-defined operation anyway. Which _levels_ of the walking cache? > Again, the size (and alignment) of the flush would actually tell you. > A new boolean "flush" parameter does *NOT* tell that at all. > > So I think this new interface is mis-named, but I also think it's > pointless. Just DTRT automatically when somebody asks for a flush that > covers a PMD range (or a PUD range). > > Linus -aneesh
