Messages in this thread | | | Date | Fri, 4 Mar 2022 14:33:26 -0800 (PST) | From | Hugh Dickins <> | Subject | Re: [PATCH mmotm] mempolicy: mbind_range() set_policy() after vma_merge() |
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On Fri, 4 Mar 2022, Oleg Nesterov wrote: > On 03/03, Hugh Dickins wrote: > > > > Just delete that optimization now (though it could be made conditional > > on vma not having a set_policy). Also remove the "next" variable: > > it turned out to be blameless, but also pointless. > > > > Fixes: 3964acd0dbec ("mm: mempolicy: fix mbind_range() && vma_adjust() interaction") > > I can't believe I ever looked at this code ;)
;)
> > Acked-by: Oleg Nesterov <oleg@redhat.com>
Thanks.
> > offtopic question... can't vma_replace_policy() check vm_ops && vm_ops->set_policy > at the start, before mpol_dup() ?
You are probably correct, though that is not how I did or would do it.
For me too, it's a long time since I've been in here: I have a large number of cleanups to mm/mempolicy.c, done in the early days of shmem huge pages (and leading up to NUMA migration outside of mmap lock), but never the time to carry them forward; and quite a few other people have made their own cleanups here too, so hard work to integrate it all.
This particular patch here stood out in my mind as an actual bugfix: our people found shmem pages being allocated on the wrong node because of it; last time I tried to work in this area, I did pull this one out and push it into our tree, before approaching any of the rest of it.
If I look at the last of our trees which had the full set of cleanups, I see that my vma_replace_policy() had less in, but mbind_range() doing what you have in mind, checking vm_ops->set_policy in between the mpol_equal() check at the top of the loop and the vma_merge() below it: with a comment "If set_policy() is implemented, the vma is nothing more than a window on to the shared object, and we do not set vm_policy and we do not split the vma" (then calls the set_policy()).
But I think that depends on other changes in other patches (not setting vm_policy): now, just as usual, I absolutely do not have the time to get back into that. So, thanks for the observation, but I have to stick with just this bugfix for now (a long now!).
It's good to hear from you, Oleg: stay well.
Hugh
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