On 19/06/25 6:38 PM, Petr Mladek wrote: > On Wed 2025-06-18 19:16:00, Pedro Falcato wrote: >> On Wed, Jun 18, 2025 at 10:44:20AM +0200, David Hildenbrand wrote: >>> On 18.06.25 10:37, Anshuman Khandual wrote: >>>> >>>> >>>> On 18/06/25 1:48 PM, David Hildenbrand wrote: >>>>> On 18.06.25 06:12, Anshuman Khandual wrote: >>>>>> Add a new format for printing page table entries. >>>>>> >>>>>> Cc: Petr Mladek <pmladek@xxxxxxxx> >>>>>> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> >>>>>> Cc: Jonathan Corbet <corbet@xxxxxxx> >>>>>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >>>>>> Cc: David Hildenbrand <david@xxxxxxxxxx> >>>>>> Cc: linux-doc@xxxxxxxxxxxxxxx >>>>>> Cc: linux-kernel@xxxxxxxxxxxxxxx >>>>>> Cc: linux-mm@xxxxxxxxx >>>>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx> >>>>>> --- >>>>>> Documentation/core-api/printk-formats.rst | 14 ++++++++++++++ >>>>>> lib/vsprintf.c | 20 ++++++++++++++++++++ >>>>>> mm/memory.c | 5 ++--- >>>>>> scripts/checkpatch.pl | 2 +- >>>>>> 4 files changed, 37 insertions(+), 4 deletions(-) >>>>>> >>>>>> diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst >>>>>> index 4b7f3646ec6ce..75a110b059ee1 100644 >>>>>> --- a/Documentation/core-api/printk-formats.rst >>>>>> +++ b/Documentation/core-api/printk-formats.rst >>>>>> @@ -689,6 +689,20 @@ Rust >>>>>> Only intended to be used from Rust code to format ``core::fmt::Arguments``. >>>>>> Do *not* use it from C. >>>>>> +Page Table Entry >>>>>> +---------------- >>>>>> + >>>>>> +:: >>>>>> + %ppte >>>>>> + >>>>>> +Print standard page table entry pte_t. >>>>>> + >>>>>> +Passed by reference. >>>>> >>>>> Curious, why the decision to pass by reference? >>>> >>>> Just to make this via %p<> based address mechanism. But wondering >>>> will it be better for the pte to be represented via value instead >>>> of reference ? >>> >>> We commonly pass ptes to functions through value, not reference, that's why >>> I am asking. >> >> >> All printf/printk extensions in the kernel follow %p<some letters> and use >> pointers because %p takes pointers, so it lets us use -Wformat with no issues. >> >> So yes, taking a pte_t * is required. > > Correct. But the pointer is usually needed because the %pxx format > need to access a structure. Right. > > Passing a pointer is another potential source of errors. I mean that > the callers might pass an invalid pointer by mistake... Agreed - could be a source of error when not used properly. > > Another aspect is performance. It is likely not a big deal for classic > printk() which is a slow path. But trace_printk() tries to optimize > the speed by deferred formatting where possible, see vbin_printf() > and bstr_printf(). > > I think that this is not a blocker for this patchset. But you should > know that using %pxx has a cost. Got it - thanks for the explanation.
