On Wed, Mar 05, 2014 at 08:06:23PM -0800, Hugh Dickins wrote: > On Wed, 5 Mar 2014, Chris Wilson wrote: > > > "When we cannot write a page we should use redirty_page_for_writepage() > > instead of plain set_page_dirty(). That tells writeback code we have > > problems, redirties only the page (redirtying buffers is not needed), > > and updates mm accounting of failed page writes." > > I didn't locate the origin of that quotation, but it's talking about > the usual filesystem cap_account_dirty/cap_account_writeback protocol. > > shmem doesn't participate it that: it only writes out (to swap) under > memory pressure, not for sync, and follows a much simpler path. Using > redirty_page_for_writepage() would lead it into complications, some of > which we prefer to avoid for efficiency, some of which would actually > be wrong (unless/until there's reason to convert shmem over to the > full protocol). > > > > > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > > So NAK. No worries, I was only concerned with that it seem to be doing magic with writeback accounting, which seemed relevant. > But you didn't explain why you want to make this change. I presume > it's for the 5/5 which you didn't Cc to me, but I've looked up on > lists.freedesktop.org/archives/intel-gfx. > > That's a bigger change and worrying: I've not thought through > the consequences of shmem page writeback from generic_writepages() > called from within a slab shrinker: we're used to doing shmem page > writeback from pageout() in mm/vmscan.c and nowhere else. > > One thing that would certainly be wrong (liable to deadlock) would > be to do that when shrink_control's gfp_mask does not have __GFP_IO. > But I'm not comfortable with page writeback from this level at all. > > The shmem_truncate_range() (you've had for a long time) should be safe, > and the new invalidate_mapping_pages() too: neither of those gets into > I/O, and invalidate_mapping_pages() looks as if it does all that's > necessary for those pages to be put under writeback at the next > shrink_inactive_list() of the lruvec. > > Or perhaps there's a gotcha or two, which we can fix up. > But please try to stick to truncation and invalidation. Thank you for your feedback. I am just trying to poke things to understand how we manage to end up calling oom-killer with an empty swap. My presumption was that we were failing to trigger writeback. I shall see how we fare with just invalidating the inode. -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
