On 08/03/14 at 11:08 -0500, Theodore Ts'o wrote: > On Wed, Mar 05, 2014 at 03:13:43PM +0100, Lucas Nussbaum wrote: > > TL;DR: we experience long temporary hangs when doing multiple mount -o > > remount at the same time as other I/O on an ext4 filesystem. > > > > When starting hundreds of LXC containers simultaneously on a system, the > > boot of some containers was hanging. We tracked this down to an > > initscript's use of mount -o remount, which was hanging in D state. > > > > We reproduced the problem outside of LXC, with the script available at > > [0]. That script initiates 1000 mount -o remount, and performs some > > writes using a big cp to the same filesystem during the remounts.... > > +linux-fsdevel since the patch modifies fs/super.c > > Lukas, can you try this patch? I'm pretty sure this is what's going > on. It turns out each "mount -o remount" is implying an fsync(), so > your test case is identical to copying a large file while having > thousand of processes calling syncfs() on the file system, with the > predictable results. Hi Ted, I can confirm that: 1) the patch solves my problem 2) issuing 'sync' instead of 'mount -o remount' indeed exhibits the problem again However, I'm curious: why would such a workload (multiple syncfs() initiated during a write) block for several minutes on an ext4 filesystem? I've just tried again on ext3, and it's not a problem in that case. Lucas -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
