On Thu, May 08, 2014 at 10:12:40AM -0700, John Stultz wrote: > On 04/29/2014 02:21 PM, John Stultz wrote: > > Another few weeks and another volatile ranges patchset... > > > > After getting the sense that the a major objection to the earlier > > patches was the introduction of a new syscall (and its somewhat > > strange dual length/purged-bit return values), I spent some time > > trying to rework the vma manipulations so we can be we won't fail > > mid-way through changing volatility (basically making it atomic). > > I think I have it working, and thus, there is no longer the > > need for a new syscall, and we can go back to using madvise() > > to set and unset pages as volatile. > > Johannes: To get some feedback, maybe I'll needle you directly here a > bit. :) > > Does moving this interface to madvise help reduce your objections? I > feel like your cleaning-the-dirty-bit idea didn't work out, but I was > hoping that by reworking the vma manipulations to be atomic, we could > move to madvise and still avoid the new syscall that you seemed bothered > by. But I've not really heard much from you recently so I worry your > concerns on this were actually elsewhere, and I'm just churning the > patch needlessly. My objection was not the syscall. >From a reclaim perspective, using the dirty state to denote whether a swap-backed page needs writeback before reclaim is quite natural and I much prefer Minchan's changes to the reclaim code over yours. >From an interface point of view, I would prefer the simplicity of cleaning dirty bits to invalidate pages, and a default of zero-filling invalidated pages instead of sending SIGBUS. This also is quite natural when you think of anon/shmem mappings as cache pages on top of /dev/zero (see mmap_zero() and shmem_zero_setup()). And it translates well to tmpfs. At the same time, I acknowledge that there are usecases that want SIGBUS delivery for more than just convenience in order to implement userspace fault handling, and this is the only place where I see a real divergence in actual functionality from Minchan's code. That, however, truly is a separate virtual memory feature. Would it be possible for you to take MADV_FREE and MADV_REVIVE as a base and implement an madvise op that switches the no-page behavior of a VMA from zero-filling to SIGBUS delivery? -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>