lkml.org 
[lkml]   [2007]   [Nov]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [RFC 5/7] LTTng instrumentation mm
    * Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca) wrote:
    > * Dave Hansen (haveblue@us.ibm.com) wrote:
    > > On Fri, 2007-11-16 at 09:47 -0500, Mathieu Desnoyers wrote:
    > > > * Dave Hansen (haveblue@us.ibm.com) wrote:
    > > > > For most (all?) architectures, the PFN and the virtual address in the
    > > > > kernel's linear are interchangeable with pretty trivial arithmetic. All
    > > > > pages have a pfn, but not all have a virtual address. Thus, I suggested
    > > > > using the pfn. What kind of virtual addresses are you talking about?
    > > > >
    > > >
    > > > Hrm, in asm-generic/memory_model.h, we have various versions of
    > > > __page_to_pfn. Normally they all cast the result to (unsigned long),
    > > > except for :
    > > >
    > > >
    > > > #elif defined(CONFIG_SPARSEMEM_VMEMMAP)
    > > >
    > > > /* memmap is virtually contigious. */
    > > > #define __pfn_to_page(pfn) (vmemmap + (pfn))
    > > > #define __page_to_pfn(page) ((page) - vmemmap)
    > > >
    > > > So I guess the result is a pointer ? Should this be expected ?
    > >
    > > Nope. 'pointer - pointer' is an integer. Just solve this equation for
    > > integer:
    > >
    > > 'pointer + integer = pointer'
    > >
    >
    > Well, using page_to_pfn turns out to be ugly in markers (and in
    > printks) then. Depending on the architecture, it will result in either
    > an unsigned long (x86_64) or an unsigned int (i386), which corresponds

    Well, it's signed long and signed int, but the point is still valid.

    > to %lu or %u and will print a warning if we don't cast it explicitly.
    >
    > Mathieu
    >
    >
    > > -- Dave
    > >
    >
    > --
    > Mathieu Desnoyers
    > Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
    > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68

    --
    Mathieu Desnoyers
    Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-11-19 20:03    [from the cache]
    ©2003-2014 Jasper Spaans. hosted at Digital Ocean