What happened to this patch? I do not see it merged for 3.19 and nor in the current mmotm tree (2014-12-15-17-05) On Wed 26-11-14 22:11:45, Konstantin Khlebnikov wrote: > Constantly forking task causes unlimited grow of anon_vma chain. > Each next child allocate new level of anon_vmas and links vmas to all > previous levels because it inherits pages from them. None of anon_vmas > cannot be freed because there might be pages which points to them. > > This patch adds heuristic which decides to reuse existing anon_vma instead > of forking new one. It counts vmas and direct descendants for each anon_vma. > Anon_vma with degree lower than two will be reused at next fork. > > As a result each anon_vma has either alive vma or at least two descendants, > endless chains are no longer possible and count of anon_vmas is no more than > two times more than count of vmas. > > Signed-off-by: Konstantin Khlebnikov <koct9i@xxxxxxxxx> > Reported-by: Daniel Forrest <dan.forrest@xxxxxxxxxxxxx> > Tested-by: Michal Hocko <mhocko@xxxxxxx> > Reviewed-by: Michal Hocko <mhocko@xxxxxxx> > Link: http://lkml.kernel.org/r/20120816024610.GA5350@xxxxxxxxxxxxxxxxxxxxxxx > Fixes: 5beb49305251 ("mm: change anon_vma linking to fix multi-process server scalability issue") > Cc: Stable <stable@xxxxxxxxxxxxxxx> (2.6.34+) > > --- > > v2: update degree in anon_vma_prepare for merged anon_vma > v3: update comment and tags > --- > include/linux/rmap.h | 16 ++++++++++++++++ > mm/rmap.c | 30 +++++++++++++++++++++++++++++- > 2 files changed, 45 insertions(+), 1 deletion(-) > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index c0c2bce..b1d140c 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -45,6 +45,22 @@ struct anon_vma { > * mm_take_all_locks() (mm_all_locks_mutex). > */ > struct rb_root rb_root; /* Interval tree of private "related" vmas */ > + > + /* > + * Count of child anon_vmas and VMAs which points to this anon_vma. > + * > + * This counter is used for making decision about reusing old anon_vma > + * instead of forking new one. It allows to detect anon_vmas which have > + * just one direct descendant and no vmas. Reusing such anon_vma not > + * leads to significant preformance regression but prevents degradation > + * of anon_vma hierarchy to endless linear chain. > + * > + * Root anon_vma is never reused because it is its own parent and it has > + * at leat one vma or child, thus at fork it's degree is at least 2. > + */ > + unsigned degree; > + > + struct anon_vma *parent; /* Parent of this anon_vma */ > }; > > /* > diff --git a/mm/rmap.c b/mm/rmap.c > index 19886fb..df5c44e 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -72,6 +72,8 @@ static inline struct anon_vma *anon_vma_alloc(void) > anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL); > if (anon_vma) { > atomic_set(&anon_vma->refcount, 1); > + anon_vma->degree = 1; /* Reference for first vma */ > + anon_vma->parent = anon_vma; > /* > * Initialise the anon_vma root to point to itself. If called > * from fork, the root will be reset to the parents anon_vma. > @@ -188,6 +190,8 @@ int anon_vma_prepare(struct vm_area_struct *vma) > if (likely(!vma->anon_vma)) { > vma->anon_vma = anon_vma; > anon_vma_chain_link(vma, avc, anon_vma); > + /* vma link if merged or child link for new root */ > + anon_vma->degree++; > allocated = NULL; > avc = NULL; > } > @@ -256,7 +260,17 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src) > anon_vma = pavc->anon_vma; > root = lock_anon_vma_root(root, anon_vma); > anon_vma_chain_link(dst, avc, anon_vma); > + > + /* > + * Reuse existing anon_vma if its degree lower than two, > + * that means it has no vma and just one anon_vma child. > + */ > + if (!dst->anon_vma && anon_vma != src->anon_vma && > + anon_vma->degree < 2) > + dst->anon_vma = anon_vma; > } > + if (dst->anon_vma) > + dst->anon_vma->degree++; > unlock_anon_vma_root(root); > return 0; > > @@ -279,6 +293,9 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) > if (!pvma->anon_vma) > return 0; > > + /* Drop inherited anon_vma, we'll reuse old one or allocate new. */ > + vma->anon_vma = NULL; > + > /* > * First, attach the new VMA to the parent VMA's anon_vmas, > * so rmap can find non-COWed pages in child processes. > @@ -286,6 +303,10 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) > if (anon_vma_clone(vma, pvma)) > return -ENOMEM; > > + /* An old anon_vma has been reused. */ > + if (vma->anon_vma) > + return 0; > + > /* Then add our own anon_vma. */ > anon_vma = anon_vma_alloc(); > if (!anon_vma) > @@ -299,6 +320,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) > * lock any of the anon_vmas in this anon_vma tree. > */ > anon_vma->root = pvma->anon_vma->root; > + anon_vma->parent = pvma->anon_vma; > /* > * With refcounts, an anon_vma can stay around longer than the > * process it belongs to. The root anon_vma needs to be pinned until > @@ -309,6 +331,7 @@ int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) > vma->anon_vma = anon_vma; > anon_vma_lock_write(anon_vma); > anon_vma_chain_link(vma, avc, anon_vma); > + anon_vma->parent->degree++; > anon_vma_unlock_write(anon_vma); > > return 0; > @@ -339,12 +362,16 @@ void unlink_anon_vmas(struct vm_area_struct *vma) > * Leave empty anon_vmas on the list - we'll need > * to free them outside the lock. > */ > - if (RB_EMPTY_ROOT(&anon_vma->rb_root)) > + if (RB_EMPTY_ROOT(&anon_vma->rb_root)) { > + anon_vma->parent->degree--; > continue; > + } > > list_del(&avc->same_vma); > anon_vma_chain_free(avc); > } > + if (vma->anon_vma) > + vma->anon_vma->degree--; > unlock_anon_vma_root(root); > > /* > @@ -355,6 +382,7 @@ void unlink_anon_vmas(struct vm_area_struct *vma) > list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) { > struct anon_vma *anon_vma = avc->anon_vma; > > + BUG_ON(anon_vma->degree); > put_anon_vma(anon_vma); > > list_del(&avc->same_vma); > > -- > 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> -- Michal Hocko SUSE Labs -- 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>