On Sun, Jan 20 2008, Boaz Harrosh wrote: > On Sun, Jan 20 2008 at 21:29 +0200, Jens Axboe <jens.axboe@xxxxxxxxxx> wrote: > > On Sun, Jan 20 2008, James Bottomley wrote: > >> On Sun, 2008-01-20 at 21:18 +0200, Boaz Harrosh wrote: > >>> On Tue, Jan 15 2008 at 19:52 +0200, James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: > >>>> this patch depends on the sg branch of the block tree > >>>> > >>>> James > >>>> > >>>> --- > >>>> From: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> > >>>> Date: Tue, 15 Jan 2008 11:11:46 -0600 > >>>> Subject: remove use_sg_chaining > >>>> > >>>> With the sg table code, every SCSI driver is now either chain capable > >>>> or broken, so there's no need to have a check in the host template. > >>>> > >>>> Also tidy up the code by moving the scatterlist size defines into the > >>>> SCSI includes and permit the last entry of the scatterlist pools not > >>>> to be a power of two. > >>>> --- > >>> I have a theoretical problem that BUGed me from the beginning. > >>> > >>> Could it happen that a memory critical IO, (that is needed to free > >>> memory), be collected into an sg-chained large IO, and the allocation > >>> of the multiple sg-pool-allocations fail, thous dead locking on > >>> out-of-memory? Is there a mechanism in place that will split large IO's > >>> into smaller chunks in the event of out-of-memory condition in prep_fn? > >>> > >>> Is it possible to call blk_rq_map_sg() with less then what is present > >>> at request to only map the starting portion? > >> Obviously, that's why I was worrying about mempool size and default > >> blocks a while ago. > >> > >> However, the deadlock only occurs if the device is swap or backing a > >> filesystem with memory mapped files. The use cases for this are really > >> tapes and other entities that need huge buffers. That's why we're > >> keeping the system sector size at 1024 unless you alter it through sysfs > >> (here gun, there foot ...) > > > > Alternatively (and much safer, imho), we allow blk_rq_map_sg() return > > smaller than nr_phys_segments and just ensure that the request is > > continued nicely through the normal 'request if residual' logic. > > > Thats a grate Idea. I will Q it on my todo list. Thanks ok good, thanks :-) -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
