Messages in this thread | | | From | Rasmus Villemoes <> | Subject | Re: [RFC][PATCH] procfs: Add /proc/<pid>/mapped_files | Date | Wed, 14 Jan 2015 15:53:16 +0100 |
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On Wed, Jan 14 2015, Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com> wrote:
> On 14 January 2015 at 19:43, Rasmus Villemoes <linux@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
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