On Wed, 29 Feb 2012, Johannes Weiner wrote: > > Saving the begin/end_update_page_stat() calls for the anon case where > we know in advance we don't need them is one thing, but this also > hides a dependencies that even eludes lockdep behind what looks like a > minor optimization of the anon case. Sounds like you'd appreciate a comment there: akpm has not put this version in yet, so I'll send an updated version shortly. > > Wouldn't this be more robust if we turned the ordering inside out in > move_account instead? I think we need more than the one user of this infrastructure before that can be decided. But I didn't actually consider that at all: perhaps prejudiced by the way I had solved the race Konstantin pointed out in my patchset of 10 last week, by using the lruvec lock for move_lock_mem_cgroup too, which fits with it being inside the page_cgroup lock. Hmm, I notice move_lock_mem_cgroup is likewise spin_lock_irqsave: if it needs to be (and I guess the idea is that it doesn't need to be today, but for generality later on had better be), then it has to be inside page_cgroup lock. (If FILE_MAPPED were to be the only user of the infrastructure, I'd actually prefer to remove the begin/end, and make move_account raise the file page's mapcount temporarily, doing its own page_remove_rmap after, to solve these races. There's probably one or two VM_BUG_ONs elsewhere that would need deleting to make that completely safe. But I understand there may be more users to come - and mapcount games might not fit your desire for robustness.) Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>