On Wed, Jan 05, 2011 at 01:12:25PM -0500, Trond Myklebust wrote: > On Wed, 2011-01-05 at 17:26 +0000, Russell King - ARM Linux wrote: > > On Wed, Jan 05, 2011 at 12:17:27PM -0500, Trond Myklebust wrote: > > > We should already be flushing the kernel direct mapping after writing by > > > means of the calls to flush_dcache_page() in xdr_partial_copy_from_skb() > > > and all the helpers in net/sunrpc/xdr.c. > > > > Hmm, we're getting into the realms of what flush_dcache_page() is supposed > > to do and what it's not supposed to do. > > > > Is this page an associated with a mapping (iow, page_mapping(page) is non- > > NULL)? If not, flush_dcache_page() won't do anything, and from my > > understanding, its flush_anon_page() which you want to be using there > > instead. > > Actually, none of these pages are ever mapped into userspace, nor are > they mapped into the page cache. > > They are allocated directly using alloc_page() by the thread that called > the readdir() syscall, so afaics there should be no incoherent mappings > other than the kernel direct mapping and the one created by > vm_map_ram(). > > So, yes, you are right that we don't need the flush_dcache_page() here. I do still think you need _something_ there, otherwise data can remain in the direct map alias and not be visible via the vmap alias. I don't see that we have anything in place to handle this at present though. jejb mentioned something about making kunmap_atomic() always flush the cache, even for lowmem pages, but I think that's going to be exceedingly painful, to the extent that I believe it will prevent our PIO-only MMC drivers working - or we need a scatterlist API that will let drivers iterate over the scatterlist without needing to continually kmap_atomic and kunmap_atomic each page. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
