On Fri, Aug 27, 2021 at 12:18:58PM -0700, Suren Baghdasaryan wrote: > While forking a process with high number (64K) of named anonymous vmas the > overhead caused by strdup() is noticeable. Experiments with ARM64 Android > device show up to 40% performance regression when forking a process with > 64k unpopulated anonymous vmas using the max name lengths vs the same > process with the same number of anonymous vmas having no name. > Introduce anon_vma_name refcounted structure to avoid the overhead of > copying vma names during fork() and when splitting named anonymous vmas. > When a vma is duplicated, instead of copying the name we increment the > refcount of this structure. Multiple vmas can point to the same > anon_vma_name as long as they increment the refcount. The name member of > anon_vma_name structure is assigned at structure allocation time and is > never changed. If vma name changes then the refcount of the original > structure is dropped, a new anon_vma_name structure is allocated > to hold the new name and the vma pointer is updated to point to the new > structure. > With this approach the fork() performance regressions is reduced 3-4x > times and with usecases using more reasonable number of VMAs (a few > thousand) the regressions is not measurable. I like the refcounting; thank you! Since patch2 adds a lot of things that are changed by patch3; maybe combine them? -- Kees Cook
