On Fri, 14 Nov 2014 10:30:53 -0600 Daniel Forrest <dan.forrest@xxxxxxxxxxxxx> wrote: > There have been a couple of inquiries about the status of this patch > over the last few months, so I am going to try pushing it out. > > Andrea Arcangeli has commented: > > > Agreed. The only thing I don't like about this patch is the hardcoding > > of number 5: could we make it a variable to tweak with sysfs/sysctl so > > if some weird workload arises we have a tuning tweak? It'd cost one > > cacheline during fork, so it doesn't look excessive overhead. > > Adding this is beyond my experience level, so if it is required then > someone else will have to make it so. > > Rik van Riel has commented: > > > I believe we should just merge that patch. > > > > I have not seen any better ideas come by. > > > > The comment should probably be fixed to reflect the > > chain length of 5 though :) > > So here is Michel's patch again with "(length > 1)" modified to > "(length > 5)" and fixed comments. > > I have been running with this patch (with the threshold set to 5) for > over two years now and it does indeed solve the problem. > > --- > > anon_vma_clone() is modified to return the length of the existing > same_vma anon vma chain, and we create a new anon_vma in the child > if it is more than five forks after the anon_vma was created, as we > don't want the same_vma chain to grow arbitrarily large. hoo boy, what's going on here. - Under what circumstances are we seeing this slab windup? - What are the consequences? Can it OOM the machine? - Why is this occurring? There aren't an infinite number of vmas, so there shouldn't be an infinite number of anon_vmas or anon_vma_chains. - IOW, what has to be done to fix this properly? - What are the runtime consequences of limiting the length of the chain? > ... > > @@ -331,10 +334,17 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) > * First, attach the new VMA to the parent VMA's anon_vmas, > * so rmap can find non-COWed pages in child processes. > */ > - if (anon_vma_clone(vma, pvma)) > + length = anon_vma_clone(vma, pvma); > + if (length < 0) > return -ENOMEM; This should propagate the anon_vma_clone() return val instead of assuming ENOMEM. But that won't fix anything... > + else if (length > 5) > + return 0; > > - /* Then add our own anon_vma. */ > + /* > + * Then add our own anon_vma. We do this only for five forks after > + * the anon_vma was created, as we don't want the same_vma chain to > + * grow arbitrarily large. > + */ > anon_vma = anon_vma_alloc(); -- 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>