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 ldWtdesn 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 13 Aug 2025, at 9:55, 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 > --- > 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 automatica= lly 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_DIS= ABLE`` > +and ``PR_GET_THP_DISABLE`` pair of prctl(2) calls. The THP behaviour s= et using > +``PR_SET_THP_DISABLE`` is inherited across fork(2) and execve(2). Thes= e calls > +support the following arguments:: > + > + 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. > + > + 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) o= r > + MADV_COLLAPSE is used. It is better to change the above sentence to: madvise(..., MADV_HUGEPAGE) or madvise(..., MADV_COLLAPSE) is used. Since this document is for sysadmin, who does not need to know the implem= entation details like VM_HUGEPAGE. And I do not see any kernel internal is mention= ed in the rest of the document. > + - 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_NOHUGEPAG= E is > + set on an area. The same for the above sentence. Something like: Note that MADV_COLLAPSE is always rejected if madvise(..., MADV_NOHUGEPAG= E) is used. > + > + prctl(PR_SET_THP_DISABLE, 0, 0, 0, 0): > + This will re-enabled THPs for the process, as if they would never ha= ve s/re-enabled/re-enable/ > + been disabled. Whether THPs will actually be used depends on global = THP > + controls. and madvise() calls. > + > + prctl(PR_GET_THP_DISABLE, 0, 0, 0, 0): > + This returns a value whose bit indicate how THP-disable is configure= d: s/bit/bits > + 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. > + > Khugepaged controls > ------------------- > > -- = > 2.47.3 Otherwise, LGTM. Reviewed-by: Zi Yan Best Regards, Yan, Zi