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. -- 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
