On Wed, Sep 08, 2021 at 05:10:23PM -0700, Prakash Sangappa wrote: > A structure per thread is allocated from a page that is shared mapped > between user space and kernel as means for faster communication. This will > facilitate sharing information, Ex: per thread stats shared between kernel > and user space, that can be read by applications without the need for > making frequent system calls in latency sensitive code path. > > A new system call is added, which will allocate the shared structure and > return its mapped user address. Multiple such structures will be allocated > on a page to accommodate requests from different threads of a multithreaded > process. Available space on a page is managed using a bitmap. When a thread > exits, the shared structure is freed and can get reused for another thread > that requests the shared structure. More pages will be allocated and used > as needed based on the number of threads requesting use of shared > structures. These pages are all freed when the process exits. > > Each of these shared structures are rounded to 128 bytes. Available space > in this structure can be used to accommodate additional per thread stats, > state etc as needed. In future, if more space beyond 128 bytes, is > needed, multiple such shared structures per thread could be allocated and > managed by the kernel. Although, space in shared structure for sharing any > kind of stats or state should be sparingly used. Therefore shared structure > layout is not exposed to user space. the system call will return the > mapped user address of a specific member or nested structure within the > shared structure corresponding to stats requested, This would allow future > enhancements/changes without breaking the API. > > Signed-off-by: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx> Where is the Documentation/ABI/ entries for this new user/kernel abi that you are creating and must maintain for the next 20+ years? thanks, greg k-h
