On Tue, Jun 15, 2010 at 10:11:22AM -0400, Christoph Hellwig wrote: > On Tue, Jun 15, 2010 at 04:00:11PM +0200, Andrea Arcangeli wrote: > > collecting clean cache doesn't still satisfy the allocation), during > > allocations in direct reclaim and increase the THREAD_SIZE than doing > > this purely for stack reasons as the VM will lose reliability if we > > This basically means doubling the stack size, as you can splice together > two extremtly stack hungry codepathes in the worst case. Do you really > want order 2 stack allocations? If we were forbidden to call ->writepage just because of stack overflow yes as I don't think it's big deal with memory compaction and I see this as a too limiting design to allow ->writepage only in kernel thread. ->writepage is also called by the pagecache layer, msync etc.. not just by kswapd. But let's defer this after we have any resemblance of hard numbers of worst-case stack usage measured during the aforementioned workload, I didn't read all the details as I'm quite against this design, but I didn't see any stack usage number or any sign of stack-overflow debug triggering. I'd suggest to measure the max stack usage first and worry later. And if ->writepage is a stack hog in some fs, I'd rather see ->writepage made less stack hungry (with proper warning at runtime with debug option enabled) than vetoed. The VM itself shouldn't be a stack hog already. I don't see a particular reason why writepage should be so stuck hungry compared to the rest of the kernel, it just have to do I/O, if it requires complex data structure it should kmalloc those and stay light on stack as everybody else. And if something I'm worried more about slab shrink than ->writepage as that enters the vfs layer and then the lowlevel fs to collect the dentry, inode etc... -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
