On 09/08/2024 10:32, David Hildenbrand wrote: > On 09.08.24 11:24, Barry Song wrote: >> On Fri, Aug 9, 2024 at 5:19 PM David Hildenbrand <david@xxxxxxxxxx> wrote: >>> >>> On 08.08.24 12:16, Ryan Roberts wrote: >>>> Add thp_anon= cmdline parameter to allow specifying the default >>>> enablement of each supported anon THP size. The parameter accepts the >>>> following format and can be provided multiple times to configure each >>>> size: >>>> >>>> thp_anon=<size>[KMG]:<value> >>>> >>>> See Documentation/admin-guide/mm/transhuge.rst for more details. >>>> >>>> Configuring the defaults at boot time is useful to allow early user >>>> space to take advantage of mTHP before its been configured through >>>> sysfs. >>> >>> I suspect a khugeapged enhancement and/or kernel-config-dependant >>> defaults and/or early system settings will also be able to mitigate that >>> without getting kernel cmdlines involved in the future. >>> >>>> >>>> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >>>> --- >>>> >>>> Hi All, >>>> >>>> I've split this off from my RFC at [1] because Barry highlighted that he would >>>> benefit from it immediately [2]. There are no changes vs the version in that >>>> series. >>>> >>>> It applies against today's mm-unstable (275d686abcb59). (although I had to >>>> fix a >>>> minor build bug in stackdepot.c due to MIN() not being defined in this tree). >>>> >>>> Thanks, >>>> Ryan >>>> >>>> >>>> .../admin-guide/kernel-parameters.txt | 8 +++ >>>> Documentation/admin-guide/mm/transhuge.rst | 26 +++++++-- >>>> mm/huge_memory.c | 55 ++++++++++++++++++- >>>> 3 files changed, 82 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt >>>> b/Documentation/admin-guide/kernel-parameters.txt >>>> index bcdee8984e1f0..5c79b58c108ec 100644 >>>> --- a/Documentation/admin-guide/kernel-parameters.txt >>>> +++ b/Documentation/admin-guide/kernel-parameters.txt >>>> @@ -6631,6 +6631,14 @@ >>>> <deci-seconds>: poll all this frequency >>>> 0: no polling (default) >>>> >>>> + thp_anon= [KNL] >>>> + Format: <size>[KMG]:always|madvise|never|inherit >>>> + Can be used to control the default behavior of the >>>> + system with respect to anonymous transparent hugepages. >>>> + Can be used multiple times for multiple anon THP sizes. >>>> + See Documentation/admin-guide/mm/transhuge.rst for more >>>> + details. >>>> + >>>> threadirqs [KNL,EARLY] >>>> Force threading of all interrupt handlers except those >>>> marked explicitly IRQF_NO_THREAD. >>>> diff --git a/Documentation/admin-guide/mm/transhuge.rst >>>> b/Documentation/admin-guide/mm/transhuge.rst >>>> index 24eec1c03ad88..f63b0717366c6 100644 >>>> --- a/Documentation/admin-guide/mm/transhuge.rst >>>> +++ b/Documentation/admin-guide/mm/transhuge.rst >>>> @@ -284,13 +284,27 @@ that THP is shared. Exceeding the number would block >>>> the collapse:: >>>> >>>> A higher value may increase memory footprint for some workloads. >>>> >>>> -Boot parameter >>>> -============== >>>> +Boot parameters >>>> +=============== >>>> >>>> -You can change the sysfs boot time defaults of Transparent Hugepage >>>> -Support by passing the parameter ``transparent_hugepage=always`` or >>>> -``transparent_hugepage=madvise`` or ``transparent_hugepage=never`` >>>> -to the kernel command line. >>>> +You can change the sysfs boot time default for the top-level "enabled" >>>> +control by passing the parameter ``transparent_hugepage=always`` or >>>> +``transparent_hugepage=madvise`` or ``transparent_hugepage=never`` to the >>>> +kernel command line. >>>> + >>>> +Alternatively, each supported anonymous THP size can be controlled by >>>> +passing ``thp_anon=<size>[KMG]:<state>``, where ``<size>`` is the THP size >>>> +and ``<state>`` is one of ``always``, ``madvise``, ``never`` or >>>> +``inherit``. >>>> + >>>> +For example, the following will set 64K THP to ``always``:: >>>> + >>>> + thp_anon=64K:always >>>> + >>>> +``thp_anon=`` may be specified multiple times to configure all THP sizes as >>>> +required. If ``thp_anon=`` is specified at least once, any anon THP sizes >>>> +not explicitly configured on the command line are implicitly set to >>>> +``never``. >>> >>> I suggest documenting that "thp_anon=" will not effect the value of >>> "transparent_hugepage=", or any configured default. Did you see the previous conversation with Barry about whether or not to honour configured defaults when any thp_anon= is provided [1]? Sounds like you also think we should honour the PMD "inherit" default if not explicitly provided on the command line? (see link for justification for the approach I'm currently taking). [1] https://lore.kernel.org/linux-mm/CAGsJ_4x8ruPspuk_FQVggJMWcXLbRuZFq44gg-Dt7Ewt3ExqTw@xxxxxxxxxxxxxx/ >>> >>> Wondering if a syntax like >>> >>> thp_anon=16K,32K,64K:always;1048K,2048K:madvise Are there examples of that syntax already or have you just made it up? I found examples with the colon (:) but nothing this fancy. I guess that's not a reason not to do it though (other than the risk of screwing up the parser in a subtle way). >>> >>> (one could also support ranges, like "16K-64K") >>> >>> Would be even better. Then, maybe only allow a single instance. >>> >>> Maybe consider it if it's not too crazy to parse ;) I'll take a look. I'm going to be out for 3 weeks from end of Monday though, so probably won't get around to that until I'm back. I know Barry is keen to get this merged, so Barry, if you'd like to take it over that's fine by me (I'm sure you have enough on your plate though). >> >> I prefer the current approach because it effectively filters cases like this. >> >> [ 0.000000] huge_memory: thp_anon=8K:inherit: cannot parse, ignored >> [ 0.000000] Unknown kernel command line parameters >> "thp_anon=8K:inherit", will be passed to user space. >> >> if we put multiple sizes together, 8K,32K,64K:always >> >> We can't determine whether this command line is legal or illegal as it >> is partially legal and partially illegal. > > Besides: I wouldn't bother about this "user does something stupid" scenario that > much. > > But yes, once we support more sizes a cmdline might turn invalid on an older > kernel. > > However, I don't see the problem here. User passed a non-existant size. Ignore > that one but handle the others, like you would with multiple commands? Yep, the parser could emit a warning for the size and move on. > > It can be well defined and documented. The command line is legal, just one size > does not exist. > > The world will continue turning :) >
