On Fri, Jan 16, 2009 at 02:51:19PM +0900, MinChan Kim wrote: > On Thu, Jan 15, 2009 at 10:33:38PM -0700, Matthew Wilcox wrote: > > On Fri, Jan 16, 2009 at 02:28:04PM +0900, MinChan Kim wrote: > > > Now, Anyone don't maintain cramfs. > > > I don't know who is maintain romfs. so I send this patch to linux-mm, > > > lkml, linux-dev. > > > > > > I am not sure my thought is right. > > > > > > When readpage is called, page with argument in readpage is just new > > > allocated because kernel can't find that page in page cache. > > > > > > At this time, any user process can't map the page to their address space. > > > so, I think D-cache aliasing probelm never occur. > > > > > > It make sense ? > > > > Sorry, no. You have to call fluch_dcache_page() in two situations -- > > when the kernel is going to read some data that userspace wrote, *and* > > when userspace is going to read some data that the kernel wrote. From a > > quick look at the patch, this seems to be the second case. The kernel > > wrote data to a pagecache page, and userspace should be able to read it. > > > > To understand why this is necessary, consider a processor which is > > virtually indexed and has a writeback cache. The kernel writes to a > > page, then a user process reads from the same page through a different > > address. The cache doesn't find the data the kernel wrote because it > > has a different virtual index, so userspace reads stale data. > > I see. :) > > Thanks for quick reponse and good explaination. > Hmm,.. one more question. > > I can't find flush_dcache_page call in mpage_readpage which is > generic read function. In case of ext fs, it use mpage_readpage > with readpage. > > who and where call flush_dcache_page in mpage_readpage call path? I think if the page is populated via IO, then it is responsibility of the IO layers (eg dma API) to ensure caches are consistent. Presumably this would include calling flush_dcache_page if we CPU is being used for the copies (eg. see drivers/block/brd.c). But there are quite possibly holes around here because not as much testing is done on CPUs with these kinds of caches. Eg. brd probably should be doing a flush_dcache_page in the rw == WRITE direction AFAIKS, so it picks up user aliases here. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
