On Wed, 2010-02-17 at 20:44 +0000, Russell King - ARM Linux wrote: > No, because that'd probably bugger up the Sparc64 method of delaying > flush_dcache_page. > > This method works as follows: > > - a page cache page is allocated - this has PG_arch_1 clear. > > - IO happens on it and it's placed into the page cache. PG_arch_1 is > still clear. > > - someone calls read()/write() which accesses the page. The generic > file IO layers call flush_dcache_page() in response to > read()/write() > fs calls. flush_dcache_page() spots that the page is not yet mapped > into userspace, and sets PG_arch_1 to mark the fact that the kernel > mapping is dirty. > > - when someone maps the page, we check PG_arch_1 in update_mmu_cache. > If PG_arch_1 is set, we flush the kernel mapping. > > Clearly, if we go around having drivers clearing PG_arch_1, this is > going to break horribly. Ok, you do things very differently than us on ppc then. We clear PG_arch_1 in flush_dcache_page(), and we set it when the page has been cache cleaned for execution. We assume that anybody that dirties a page in the kernel will call flush_dcache_page() which removes our PG_arch_1 bit thus marking the page "dirty". Note that from experience, doing the check & flushes in update_mmu_cache() is racy on SMP. At least for I$/D$, we have the case where processor one does set_pte followed by update_mmu_cache(). The later isn't done yet but processor 2 sees the PTE now and starts using it, cache hasn't been fully flushed yet. You may avoid that race in some ways, but on ppc, I've stopped using that. I now do things directly in set_pte_at(). In fact, that's why I want your patch to change update_mmu_cache() to take a PTE pointer :-) Since my set_pte_at() can now remove the _PAGE_EXEC bit, I need update_mmu_cache() to re-read the PTE before it updates the hash table or TLB. Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
