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Message-ID: <CAGsJ_4wMZbRAYDzu9QVZDeu2WS9zfLH4r9yVqXHu2UsZiG0RKQ@mail.gmail.com>
Date: Fri, 1 Nov 2024 11:16:05 +1300
From: Barry Song <21cnbao@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: Maíra Canal <mcanal@...lia.com>,
Jonathan Corbet <corbet@....net>, Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>, Ryan Roberts <ryan.roberts@....com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>, Lance Yang <ioworker0@...il.com>, linux-mm@...ck.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-dev@...lia.com
Subject: Re: [PATCH v3 3/4] mm: shmem: override mTHP shmem default with a
kernel parameter
On Fri, Nov 1, 2024 at 10:39 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 31.10.24 22:12, Barry Song wrote:
> > On Fri, Nov 1, 2024 at 3:20 AM Maíra Canal <mcanal@...lia.com> wrote:
> >>
> >> On 31/10/24 10:33, David Hildenbrand wrote:
> >>> On 31.10.24 14:24, Maíra Canal wrote:
> >>>> Hi David,
> >>>>
> >>>> On 31/10/24 09:57, David Hildenbrand wrote:
> >>>>> On 31.10.24 13:51, Maíra Canal wrote:
> >>>>>> Hi David,
> >>>>>>
> >>>>>> On 31/10/24 09:37, David Hildenbrand wrote:
> >>>>>>> On 30.10.24 13:58, Maíra Canal wrote:
> >>>>>>>> Add the ``thp_shmem=`` kernel command line to allow specifying the
> >>>>>>>> default policy of each supported shmem hugepage size. The kernel
> >>>>>>>> parameter
> >>>>>>>> accepts the following format:
> >>>>>>>>
> >>>>>>>> thp_shmem=<size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-
> >>>>>>>> <size>[KMG]:<policy>
> >>>>>>>>
> >>>>>>>> For example,
> >>>>>>>>
> >>>>>>>> thp_shmem=16K-64K:always;128K,512K:inherit;256K:advise;1M-2M:never;4M-8M:within_size
> >>>>>>>>
> >>>>>>>> By configuring the default policy of several shmem hugepages, the
> >>>>>>>> user
> >>>>>>>> can take advantage of mTHP before it's been configured through sysfs.
> >>>>>>>>
> >>>>>>>> Signed-off-by: Maíra Canal <mcanal@...lia.com>
> >>>>>>>> ---
> >>>>>>>> .../admin-guide/kernel-parameters.txt | 10 ++
> >>>>>>>> Documentation/admin-guide/mm/transhuge.rst | 17 +++
> >>>>>>>> mm/shmem.c | 109 +++++++++++++
> >>>>>>>> ++++-
> >>>>>>>> 3 files changed, 135 insertions(+), 1 deletion(-)
> >>>>>>>>
> >>>>>>
> >>>>>> [...]
> >>>>>>
> >>>>>>>> diff --git a/mm/shmem.c b/mm/shmem.c
> >>>>>>>> index dfcc88ec6e34..c2299fa0b345 100644
> >>>>>>>> --- a/mm/shmem.c
> >>>>>>>> +++ b/mm/shmem.c
> >>>>>>>> @@ -136,6 +136,7 @@ static unsigned long huge_shmem_orders_always
> >>>>>>>> __read_mostly;
> >>>>>>>> static unsigned long huge_shmem_orders_madvise __read_mostly;
> >>>>>>>> static unsigned long huge_shmem_orders_inherit __read_mostly;
> >>>>>>>> static unsigned long huge_shmem_orders_within_size __read_mostly;
> >>>>>>>> +static bool shmem_orders_configured __initdata;
> >>>>>>>> #endif
> >>>>>>>> #ifdef CONFIG_TMPFS
> >>>>>>>> @@ -5027,7 +5028,8 @@ void __init shmem_init(void)
> >>>>>>>> * Default to setting PMD-sized THP to inherit the global
> >>>>>>>> setting and
> >>>>>>>> * disable all other multi-size THPs.
> >>>>>>>> */
> >>>>>>>> - huge_shmem_orders_inherit = BIT(HPAGE_PMD_ORDER);
> >>>>>>>> + if (!shmem_orders_configured)
> >>>>>>>> + huge_shmem_orders_inherit = BIT(HPAGE_PMD_ORDER);
> >>>>>>>> #endif
> >>>>>>>> return;
> >>>>>>>> @@ -5180,6 +5182,26 @@ struct kobj_attribute
> >>>>>>>> thpsize_shmem_enabled_attr =
> >>>>>>>> #if defined(CONFIG_TRANSPARENT_HUGEPAGE)
> >>>>>>>> +static inline int get_order_from_str(const char *size_str)
> >>>>>>>> +{
> >>>>>>>> + unsigned long size;
> >>>>>>>> + char *endptr;
> >>>>>>>> + int order;
> >>>>>>>> +
> >>>>>>>> + size = memparse(size_str, &endptr);
> >>>>>>>> +
> >>>>>>>> + if (!is_power_of_2(size))
> >>>>>>>> + goto err;
> >>>>>>>> + order = get_order(size);
> >>>>>>>> + if (BIT(order) & ~THP_ORDERS_ALL_FILE_DEFAULT)
> >>>>>>>> + goto err;
> >>>>>>>> +
> >>>>>>>> + return order;
> >>>>>>>> +err:
> >>>>>>>> + pr_err("invalid size %s in thp_shmem boot parameter\n",
> >>>>>>>> size_str);
> >>>>>>>> + return -EINVAL;
> >>>>>>>> +}
> >>>>>>>
> >>>>>>> Hm, mostly copy and paste. You could reuse existing
> >>>>>>> get_order_from_str()
> >>>>>>> simply by passing in the supported orders and moving error
> >>>>>>> reporting to
> >>>>>>> the caller.
> >>>>>>>
> >>>>>>
> >>>>>> Can I use functions from mm/huge_memory.c here?
> >>>>>
> >>>>> Yes, that's the idea.
> >>>>>
> >>>>
> >>>> Unfortunately, it isn't possible without adding the function to a
> >>>> header.
> >>>
> >>> Well ... sure, what's the problem with that?
> >>
> >> David & Barry, how do you feel about adding `get_order_from_str()` to
> >> lib/cmdline.c?
> >
> > I'd vote to leave it as is. If, at some point, the controls for shared memory
> > and anonymous memory are moved to a file, that would be the right time
> > to call the same get_order_from_str() for both.
> > > This is too trivial to warrant being an exposed API in huge_memory.h
> > or cmdline.
>
> I ... don't quite agree. cmdline.c is probably a bit excessive and I
> wouldn't suggest that at this point.
>
> This seems like a reasonable helper function to have as inline in
> mm/internal.h.
For get_order_from_str() specifically, I agree that it's fine to keep
it in internal.h,
as it could be considered a general need. However, anything larger than that
in parse bootcmd seems too trivial and not general enough to qualify as an API.
>
> ... unless I am missing something important and the obvious code
> duplication is warranted.
>
> --
> Cheers,
>
> David / dhildenb
>
Thanks
barry
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