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. -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
