Messages in this thread | | | Date | Fri, 27 Jan 2006 13:39:18 +0100 | From | Jens Axboe <> | Subject | Re: How to map high memory for block io |
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On Fri, Jan 27 2006, Pierre Ossman wrote: > Jens Axboe wrote: > > On Fri, Jan 27 2006, Pierre Ossman wrote: > > > >> Jens Axboe wrote: > >> > >>> On Fri, Jan 27 2006, Pierre Ossman wrote: > >>> > >>> > >>>> I'm having some problems getting high memory support to work smoothly in > >>>> my driver. The documentation doesn't indicate what I might be doing > >>>> wrong so I'll have to ask here. > >>>> > >>>> The problem seems to be that kmap & co maps a single page into kernel > >>>> memory. So when I happen to cross page boundaries I start corrupting > >>>> some unrelated parts of the kernel. I would prefer not having to > >>>> consider page boundaries in an already messy PIO loop, so I've been > >>>> trying to find either a routine to map an entire sg entry or some way to > >>>> force the block layer to not give me stuff crossing pages. > >>>> > >>>> As you can guess I have not found anything that can do what I want, so > >>>> some pointers would be nice. > >>>> > >>>> > >>> Honestly, just don't bother if you are doing PIO anyways. Just tell the > >>> block layer that you want io bounced for you instead. > >>> > >>> > >>> > >> This is the MMC layer so there is some separation between the block > >> layer and the drivers. Also, the transfers won't necessarily be from the > >> block layer so a generic solution is desired. I don't suppose there is > >> some way of accessing the bounce buffer routines in a non-bio context? > >> > > > > Only the mapping routines are appropriate at that point, or things get > > complicated. You could still do a two-page mapping, if you are careful > > about using different KMAP_ types. > > > > > > That would still make things rather difficult since there is no way to > get both maps into joining vaddrs. Is there no way to say "don't cross > page boundaries"? Setting a segment size of PAGE_SIZE still causes > problems when the offset isn't 0.
To be absolutely sure, you can just disallow multiple pages in a bio. Ala:
static int my_merge_bvec_fn(request_queue_t *q, struct bio *bio, struct bio_vec *bvec) { return 1; }
init_code() { ... blk_queue_merge_bvec(q, my_merge_bvec_fn); }
-- Jens Axboe
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