On Wed, Jan 14 2015, Siddhesh Poyarekar <siddhesh.poyare...@gmail.com> wrote:
> On 14 January 2015 at 19:43, Rasmus Villemoes <li...@rasmusvillemoes.dk> > wrote: >> Just thinking out loud: Could one simply mark a VMA as being used for >> stack during the clone call (is there room in vm_flags, or does >> VM_GROWSDOWN already tell the whole story?), and then write the TID into >> a new field in the VMA - I think one could make a union with vm_pgoff so >> as not to enlarge the structure. > > vm_flags does not have space IIRC (that was my first approach at > implementing this) and VM_GROWSDOWN is not sufficient. Looking at include/linux/mm.h: #define VM_GROWSDOWN 0x00000100 /* general info on the segment */ #define VM_PFNMAP 0x00000400 /* Page-ranges managed without "struct page", just pure PFN */ #define VM_DENYWRITE 0x00000800 /* ETXTBSY on write attempts.. */ It would seem that 0x00000200 is available (unless defined and used somewhere else). > If we can make a union with vm_pgoff like you say, we probably don't > need a flag value; a non-zero value could indicate that it is a thread > stack. Well, only when combined with checking vm_file for being NULL. One would also need to ensure that vm_pgoff is 0 for any non-stack, non-file-backed VMA. At which point it is somewhat ugly. > One problem with caching the value on clone like this though is that > the stack could change due to a setcontext, but AFAICT we don't care > about that for the process stack either. If it is important, I guess one could update the info when a task calls setcontext. Rasmus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
