On Mon, May 19, 2025 at 01:53:43PM +0200, David Hildenbrand wrote: > On 19.05.25 10:51, Lorenzo Stoakes wrote: > > When KSM-by-default is established using prctl(PR_SET_MEMORY_MERGE), this > > defaults all newly mapped VMAs to having VM_MERGEABLE set, and thus makes > > them available to KSM for samepage merging. It also sets VM_MERGEABLE in > > all existing VMAs. > > > > However this causes an issue upon mapping of new VMAs - the initial flags > > will never have VM_MERGEABLE set when attempting a merge with adjacent VMAs > > (this is set later in the mmap() logic), and adjacent VMAs will ALWAYS have > > VM_MERGEABLE set. > > Just to clarify, you mean that VM_MERGEABLE is set later, during > __mmap_new_vma()->ksm_add_vma()->__ksm_add_vma(), and we are already past > vma_merge_new_range(), correct? Yes. The self test asserts this is in fact the behaviour, and if you run it in a kernel without this patchset you can observe it in action. > > -- > Cheers, > > David / dhildenb >
