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Message-Id: <20240814085409.124466-1-21cnbao@gmail.com>
Date: Wed, 14 Aug 2024 20:54:09 +1200
From: Barry Song <21cnbao@...il.com>
To: david@...hat.com
Cc: akpm@...ux-foundation.org,
baohua@...nel.org,
baolin.wang@...ux.alibaba.com,
corbet@....net,
ioworker0@...il.com,
linux-kernel@...r.kernel.org,
linux-mm@...ck.org,
ryan.roberts@....com,
v-songbaohua@...o.com
Subject: Re: [PATCH v4] mm: Override mTHP "enabled" defaults at kernel cmdline
On Wed, Aug 14, 2024 at 8:18 PM David Hildenbrand <david@...hat.com> wrote:
>
> On 14.08.24 04:02, Barry Song wrote:
> > From: Ryan Roberts <ryan.roberts@....com>
> >
> > 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>,<size>[KMG]:<value>;<size>-<size>[KMG]:<value>
> >
> > An example:
> >
> > thp_anon=16K-64K:always;128K,512K:inherit;256K:madvise;1M-2M:never
> >
> > 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.
> >
> > Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> > Co-developed-by: Barry Song <v-songbaohua@...o.com>
> > Signed-off-by: Barry Song <v-songbaohua@...o.com>
> > ---
> > -v4:
> > * use bitmap APIs to set and clear bits. thanks very much for
> > David's comment!
> >
> > .../admin-guide/kernel-parameters.txt | 9 ++
> > Documentation/admin-guide/mm/transhuge.rst | 37 +++++--
> > mm/huge_memory.c | 96 ++++++++++++++++++-
> > 3 files changed, 134 insertions(+), 8 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index f0057bac20fb..d0d141d50638 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -6629,6 +6629,15 @@
> > <deci-seconds>: poll all this frequency
> > 0: no polling (default)
> >
> > + thp_anon= [KNL]
> > + Format: <size>,<size>[KMG]:<state>;<size>-<size>[KMG]:<state>
> > + state is one of "always", "madvise", "never" or "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 7072469de8a8..528e1a19d63f 100644
> > --- a/Documentation/admin-guide/mm/transhuge.rst
> > +++ b/Documentation/admin-guide/mm/transhuge.rst
> > @@ -284,13 +284,36 @@ that THP is shared. Exceeding the number would block the collapse::
> >
> > A higher value may increase memory footprint for some workloads.
> >
> > -Boot parameter
> > -==============
> > -
> > -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.
> > +Boot parameters
> > +===============
> > +
> > +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>,<size>[KMG]:<state>;<size>-<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 16K, 32K, 64K THP to ``always``,
> > +set 128K, 512K to ``inherit``, set 256K to ``madvise`` and 1M, 2M
> > +to ``never``::
> > +
> > + thp_anon=16K-64K:always;128K,512K:inherit;256K:madvise;1M-2M:never
> > +
> > +``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``.
> > +
> > +``transparent_hugepage`` setting only affects the global toggle. If
> > +``thp_anon`` is not specified, PMD_ORDER THP will default to ``inherit``.
> > +However, if a valid ``thp_anon`` setting is provided by the user, the
> > +PMD_ORDER THP policy will be overridden. If the policy for PMD_ORDER
> > +is not defined within a valid ``thp_anon``, its policy will default to
> > +``never``.
> >
> > Hugepages in tmpfs/shmem
> > ========================
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 1a12c011e2df..c5f4e97b49de 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -81,6 +81,7 @@ unsigned long huge_zero_pfn __read_mostly = ~0UL;
> > unsigned long huge_anon_orders_always __read_mostly;
> > unsigned long huge_anon_orders_madvise __read_mostly;
> > unsigned long huge_anon_orders_inherit __read_mostly;
> > +static bool anon_orders_configured;
> >
> > unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
> > unsigned long vm_flags,
> > @@ -737,7 +738,10 @@ static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
> > * disable all other sizes. powerpc's PMD_ORDER isn't a compile-time
> > * constant so we have to do this here.
> > */
> > - huge_anon_orders_inherit = BIT(PMD_ORDER);
> > + if (!anon_orders_configured) {
> > + huge_anon_orders_inherit = BIT(PMD_ORDER);
> > + anon_orders_configured = true;
> > + }
> >
> > *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
> > if (unlikely(!*hugepage_kobj)) {
> > @@ -922,6 +926,96 @@ static int __init setup_transparent_hugepage(char *str)
> > }
> > __setup("transparent_hugepage=", setup_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);
>
> Do we have to also test if is_power_of_2(), and refuse if not? For
> example, what if someone would pass 3K, would the existing check catch it?
no, the existing check can't catch it.
I passed thp_anon=15K-64K:always, then I got 16K enabled:
/ # cat /sys/kernel/mm/transparent_hugepage/hugepages-16kB/enabled
[always] inherit madvise never
I can actually check that by:
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 >> PAGE_SHIFT))
goto err;
order = get_order(size);
if ((1 << order) & ~THP_ORDERS_ALL_ANON)
goto err;
return order;
err:
pr_err("invalid size %s in thp_anon boot parameter\n", size_str);
return -EINVAL;
}
>
> > + order = fls(size >> PAGE_SHIFT) - 1;
>
> Is this a fancy way of writing
>
> order = log2(size >> PAGE_SHIFT);
>
> ? :)
I think ilog2 is implemented by fls ?
>
> Anyhow, if get_order() wraps that, all good.
I guess it doesn't check power of 2?
>
> > + if ((1 << order) & ~THP_ORDERS_ALL_ANON) {
> > + pr_err("invalid size %s(order %d) in thp_anon boot parameter\n",
> > + size_str, order);
> > + return -EINVAL;
> > + }
> > +
> > + return order;
> > +}
>
> Apart from that, nothing jumped at me.
Please take a look at the new get_order_from_str() before I
send v5 :-)
>
> --
> Cheers,
>
> David / dhildenb
>
Thanks
Barry
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