On Tue, Mar 29, 2011 at 03:35:17PM -0700, Andrew Morton wrote: > On Mon, 28 Mar 2011 09:57:39 -0700 > Andi Kleen <andi@xxxxxxxxxxxxxx> wrote: > > > Shaohua Li <shaohua.li@xxxxxxxxx> writes: > > > > > If we only change vma->vm_end, we can avoid taking anon_vma lock even 'insert' > > > isn't NULL, which is the case of split_vma. > > > From my understanding, we need the lock before because rmap must get the > > > 'insert' VMA when we adjust old VMA's vm_end (the 'insert' VMA is linked to > > > anon_vma list in __insert_vm_struct before). > > > But now this isn't true any more. The 'insert' VMA is already linked to > > > anon_vma list in __split_vma(with anon_vma_clone()) instead of > > > __insert_vm_struct. There is no race rmap can't get required VMAs. > > > So the anon_vma lock is unnecessary, and this can reduce one locking in brk > > > case and improve scalability. > > > > Looks good to me. > > Looks way too tricky to me. > > Please review this code for maintainability. Have we documented what > we're doing as completely and as clearly as we are able? I agree the comments could be improved, but the code change looked good to me. I don't think it impacts maintainability by itself because we already do similar magic. -Andi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>