On Wed, Aug 13, 2025 at 02:55:39PM +0100, Usama Arif wrote: > This includes the PR_SET_THP_DISABLE/PR_GET_THP_DISABLE pair of > prctl calls as well the newly introduced PR_THP_DISABLE_EXCEPT_ADVISED > flag for the PR_SET_THP_DISABLE prctl call. > > Signed-off-by: Usama Arif <usamaarif642@xxxxxxxxx> LGTM, so: Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> > --- > Documentation/admin-guide/mm/transhuge.rst | 37 ++++++++++++++++++++++ > 1 file changed, 37 insertions(+) > > diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst > index 370fba1134606..fa8242766e430 100644 > --- a/Documentation/admin-guide/mm/transhuge.rst > +++ b/Documentation/admin-guide/mm/transhuge.rst > @@ -225,6 +225,43 @@ to "always" or "madvise"), and it'll be automatically shutdown when > PMD-sized THP is disabled (when both the per-size anon control and the > top-level control are "never") > > +process THP controls > +-------------------- > + > +A process can control its own THP behaviour using the ``PR_SET_THP_DISABLE`` > +and ``PR_GET_THP_DISABLE`` pair of prctl(2) calls. The THP behaviour set using > +``PR_SET_THP_DISABLE`` is inherited across fork(2) and execve(2). These calls > +support the following arguments:: Thanks that's an improvement putting the bit about fork/exec here. > + > + prctl(PR_SET_THP_DISABLE, 1, 0, 0, 0): > + This will disable THPs completely for the process, irrespective > + of global THP controls or MADV_COLLAPSE. Thanks for including MADV_COLLAPSE aspect! > + > + prctl(PR_SET_THP_DISABLE, 1, PR_THP_DISABLE_EXCEPT_ADVISED, 0, 0): > + This will disable THPs for the process except when the usage of THPs is > + advised. Consequently, THPs will only be used when: > + - Global THP controls are set to "always" or "madvise" and > + the area either has VM_HUGEPAGE set (e.g., due do MADV_HUGEPAGE) or > + MADV_COLLAPSE is used. > + - Global THP controls are set to "never" and MADV_COLLAPSE is used. This > + is the same behavior as if THPs would not be disabled on a process > + level. > + Note that MADV_COLLAPSE is currently always rejected if VM_NOHUGEPAGE is > + set on an area. > + > + prctl(PR_SET_THP_DISABLE, 0, 0, 0, 0): > + This will re-enabled THPs for the process, as if they would never have Real super nit, but could be 'as if they were never disabled'. > + been disabled. Whether THPs will actually be used depends on global THP > + controls. > + > + prctl(PR_GET_THP_DISABLE, 0, 0, 0, 0): > + This returns a value whose bit indicate how THP-disable is configured: > + Bits > + 1 0 Value Description > + |0|0| 0 No THP-disable behaviour specified. > + |0|1| 1 THP is entirely disabled for this process. > + |1|1| 3 THP-except-advised mode is set for this process. Thanks this looks great! > + > Khugepaged controls > ------------------- > > -- > 2.47.3 >
