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?
-- Cheers, David / dhildenb
