On Wed, May 12, 2010 at 7:06 AM, Jamie Lokier <jamie@xxxxxxxxxxxxx> wrote: > Catalin Marinas wrote: >> On Wed, 2010-05-12 at 12:53 +0100, Sebastian Andrzej Siewior wrote: >> > * Catalin Marinas | 2010-05-12 12:10:39 [+0100]: >> > >> > >> > --- a/drivers/ata/libata-sff.c >> > >> > +++ b/drivers/ata/libata-sff.c >> > >> > @@ -894,7 +894,7 @@ static void ata_pio_sector(struct ata_queued_cmd *qc) >> > >> > do_write); >> > >> > } >> > >> > >> > >> > - if (!do_write) >> > >> > + if (!do_write&& !PageSlab(page)) >> > >> > flush_dcache_page(page); >> > >> >> > >> I would think that check belongs inside flush_dcache_page itself, rather >> > >> than forcing every driver to include it.. >> > > >> > >Sebastian (cc'ed) reported this as well for MIPS. >> > Thx. The patch above looks what I've sent a while ago. Jeff was going to >> > merge it afaik. >> > >> > >I think it makes sense for this check to be done in the >> > >flush_dcache_page() function. >> > >> > Why should flush_dcache_page() not flush pages you tell it? >> > From Documentation/cachetlb.txt: >> > | NOTE: This routine need only be called for page cache pages >> > | which can potentially ever be mapped into the address >> > | space of a user process. So for example, VFS layer code >> > | handling vfs symlinks in the page cache need not call >> > | this interface at all. >> > >> > A page from slab or stack is not going to see the sky of user land and >> > therefore it should not be fed into flush_dcache_page(). >> >> You are right :), so fixing the driver is the best approach. > > It worries me that a driver has any knowledge of the PageSlab() flag, > though. Especially uncommented knowledge. That flag seems VM > internal, and it's conceptually iffy: Kernel code using > get_free_pages() and using that for I/O also does not see the sky of > user land. > > If all the PIO drivers have to be changed, I'd be happier with: > > flush_dcache_page_for_pio() > > which wraps the check, explains it, and provides a single place to > change if needed. Indeed.. It's obscure enough for drivers to need to worry about these details of cache flushing/invalidation at all, let alone for them to have to worry about even more obscure details.. -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
