On Mon 03-08-15 23:32:00, Hugh Dickins wrote: [...] > But I have modified it a little, I don't think you'll mind. As you > suggested yourself, I actually prefer to test may_enter_fs there, rather > than __GFP_FS: not a big deal, I certainly wouldn't want to delay the > fix if someone thinks differently; but I tend to feel that may_enter_fs > is what we already use for such decisions there, so better to use it. > (And the SwapCache case immune to ext4 or xfs IO submission pattern.) I am not opposed. This is closer to what we had before. [...] > (I was tempted to add in > my unlock_page there, that we discussed once before: but again thought > it better to minimize the fix - it is "selfish" not to unlock_page, > but I think that anything heading for deadlock on the locked page would > in other circumstances be heading for deadlock on the writeback page - > I've never found that change critical.) I agree. It would deserve a separate patch. > And I've done quite a bit of testing. The loads that hung at the > weekend have been running nicely for 24 hours now, no problem with the > writeback hang and no problem with the dcache ENOTDIR issue. Though > I've no idea of what recent VM change turned this into a hot issue. > > And more testing on the history of it, considering your stable 3.6+ > designation that I wasn't satisfied with. Getting out that USB stick > again, I find that 3.6, 3.7 and 3.8 all OOM if their __GFP_IO test > is updated to a may_enter_fs test; but something happened in 3.9 > to make it and subsequent releases safe with the may_enter_fs test. Interesting. I would have guessed that 3.12 would make a difference (as mentioned in the changelog). Why would 3.9 make a difference is not entirely clear to me. > You can certainly argue that the remote chance of a deadlock is > worse than the fair chance of a spurious OOM; but if you insist > on 3.6+, then I think it would have to go back even further, > because we marked that commit for stable itself. I suggest 3.9+. Agreed and thanks! -- Michal Hocko SUSE Labs -- 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
