On Mon, May 21, 2012 at 10:55:42AM -0700, Kent Overstreet wrote: > On Mon, May 21, 2012 at 01:17:06PM -0400, Vivek Goyal wrote: > > May be I am missing something, hence I will ask. Is punting to workqueue > > will really solve the issue raised by Neil. > > > > Due to spliting required, we will be holding some bios in the stack and > > these bios can't be submitted till further allocation from pool happens. So > > will it matter whether we are waiting for allocation in submitting process > > context or in worker thread context. > > Punting to workqueue allows all the bio splits that have already been > allocated to be submitted. > > > IOW, say you have a pool of 2 bios. We allocate 1 bio (say bio A), and submit > > it for IO (now 1 bio left in pool). Now, bio A needs to be split up, so we > > allocate bio B and submit it (pool is empty now). Now we try to submit bio > > B and this also needs to be split. There are no more free bios so we will > > wait for some to get free but none of the bios (A and B) have actually > > been submitted for IO so nothing will get freed and we have a deadlock > > (This is assuming that memory is tight enough that we are not able to do > > any allocations from the slab backing the mempool). > > You're talking about a different issue. You can't safely split a split > from the same bio pool - but this code doesn't do that since it adds a > separate bio pool for each request_queue that's only for splits. Ok, I missed the fact that there are per queue pools for bio allocation. Thanks for clarifying. Vivek -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
