Messages in this thread | | | From | (Eric W. Biederman) | Date | Wed, 24 Jun 2009 00:35:52 -0700 | Subject | Re: [merged] proctxt-update-kernel-filesystem-proctxt-documentation.patch removed from -mm tree |
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Andrew Morton <akpm@linux-foundation.org> writes:
> On Wed, 24 Jun 2009 08:45:03 +0200 Stefani Seibold <stefani@seibold.net> wrote: > >> Am Dienstag, den 23.06.2009, 23:32 -0700 schrieb Andrew Morton: >> > On Wed, 24 Jun 2009 08:20:44 +0200 Stefani Seibold <stefani@seibold.net> wrote: >> > >> > > what is with the associated >> > > procfs-provide-stack-information-for-threads-v08.patch >> > > patch? >> > > >> > > There was no real objections against this patch, so why not merge it for >> > > 2.6.31? >> > >> > Alexey pointed out that it doesn't actually work. >> >> That is not true... it works. With my patch the kernel does exactly know >> where the thread stack is and therefor it is easy to determinate the >> associated map.
Usually yes, but not in all cases.
> On Tue, 16 Jun 2009 02:33:33 +0400 Alexey Dobriyan <adobriyan@gmail.com> wrote: > >> On Mon, Jun 15, 2009 at 03:02:05PM -0700, akpm@linux-foundation.org wrote: >> > procfs-provide-stack-information-for-threads-v08.patch >> > --- a/fs/proc/array.c~procfs-provide-stack-information-for-threads-v08 >> >> > +++ a/fs/proc/array.c >> > @@ -321,6 +321,54 @@ static inline void task_context_switch_c >> > p->nivcsw); >> > } >> > >> > +static inline unsigned long get_stack_usage_in_bytes(struct vm_area_struct *vma, >> > + struct task_struct *p) >> > +{ >> > + unsigned long i; >> > + struct page *page; >> > + unsigned long stkpage; >> > + >> > + stkpage = KSTK_ESP(p) & PAGE_MASK; >> > + >> > +#ifdef CONFIG_STACK_GROWSUP >> > + for (i = vma->vm_end; i-PAGE_SIZE > stkpage; i -= PAGE_SIZE) { >> > + >> > + page = follow_page(vma, i-PAGE_SIZE, 0); >> >> How can this work? >> >> If stack page got swapped out, you'll get smaller than actual result. > > Alexey's point is that follow_page() will return NULL if it hits a > swapped-out stack page and the loop will exit, leading to an incorrect > (ie: short) return value from get_stack_usage_in_bytes(). > > Is this claim wrong?
Add to that the code is unnecessarily complicated.
The patch mixes several different changes together. It deserves being broken up into at least two patches.
I am concerned about the performance. Glibc opens /proc/self/maps in practically every application so doing something like following page tables requires testing and verifying the performance.
Eric
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