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From: Jamie Lokier on 12 May 2010 09:10 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. -- Jamie -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Robert Hancock on 12 May 2010 19:30 On Wed, May 12, 2010 at 7:06 AM, Jamie Lokier <jamie(a)shareable.org> 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-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Catalin Marinas on 13 May 2010 07:40 On Wed, 2010-05-12 at 14:06 +0100, Jamie Lokier 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. I already proposed a PIO cache flushing API on linux-arch. I tried to revive the discussion with another patch for cachetlb.txt but it hasn't drawn much interest. On ARM we are trying to change the I/D cache handling similar to IA-64 and PowerPC (PG_arch_1 would mean "clean" rather than "dirty"). With this change, my original patch to libata-sff.c can be dropped (well, other architectures may still be broken). -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Jeff Garzik on 14 May 2010 17:50
On 05/13/2010 07:30 AM, Catalin Marinas wrote: > I already proposed a PIO cache flushing API on linux-arch. I tried to > revive the discussion with another patch for cachetlb.txt but it hasn't > drawn much interest. Oh well. I'll apply the local-to-libata patch, and hope that someone else proposes a better API. Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |