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SubjectRe: [PATCH] mtd: fix mtd_blkdevs problem with caches on some architectures (2.6.31)
On Fri, 20 Nov 2009 16:37:51 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:

> Your patch fixes bascially the same problem in MTD as we have in AOE.
> And it introduces the same problem as well - pointless empty
> cache-thrashing loops on architectures for which flush_dcache_page() is
> a no-op.
>
> What would be better here would be for block core to add a new
> rq_flush_dcache_pages() and bio_flush_dcache_pages() which the drivers
> can call. Those functions would be a no-op on architectures which
> don't need them.

Do you mean something like this?

in include/linux/bio.h

#ifdef SOMETHING_LIKE_CONFIG_CPU_HAS_DCACHE_ALIAS
extern void bio_flush_dcache_pages(struct bio *bi);
#else
static inline void bio_flush_dcache_pages(struct bio *bi)
{
}
#endif /* SOMETHING_LIKE_CONFIG_CPU_HAS_DCACHE_ALIAS */
in fs/bio.c

void bio_flush_dcache_pages(struct bio *bi)
{
int i;
struct bio_vec* bvec;
rq_for_each_segment(bvec, bio, i)
flush_dcache_page(bvec->bv_page);
}
in include/linux/blkdev.h

#ifdef SOMETHING_LIKE_CONFIG_CPU_HAS_DCACHE_ALIAS
extern void rq_flush_dcache_pages(struct request *rq);
#else
static inline void rq_flush_dcache_pages(struct request *rq)
{
}
#endif
in block/blk-core.c

void rq_flush_dcache_pages(struct request *rq)
{
struct req_iterator iter;
struct bio_vec* bvec;
rq_for_each_segment(bvec, bio, iter)
flush_dcache_page(bvec->bv_page);
}
And SOMETHING_LIKE_CONFIG_CPU_HAS_DCACHE_ALIAS should be defined
in Kconfigs for each architecture that requires this fix. I think
this is good solution and if you think the same I can create the
patch.

--
Ilya Loginov <isloginov@gmail.com>


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