linux-kernel - Re: [v3 3/4] memblock: introduce MEMBLOCK_RSRV_NOINIT

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Message-Id: <AAF485D2-508B-4F96-862F-3658104E8F76@linux.dev>
Date:   Mon, 28 Aug 2023 17:18:23 +0800
From:   Muchun Song <muchun.song@...ux.dev>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Usama Arif <usama.arif@...edance.com>,
        Linux-MM <linux-mm@...ck.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>,
        fam.zheng@...edance.com, liangma@...ngbit.com,
        punit.agrawal@...edance.com
Subject: Re: [v3 3/4] memblock: introduce MEMBLOCK_RSRV_NOINIT_VMEMMAP flag



> On Aug 28, 2023, at 17:09, Mike Rapoport <rppt@...nel.org> wrote:
> 
> On Mon, Aug 28, 2023 at 04:52:10PM +0800, Muchun Song wrote:
>> 
>> 
>> On 2023/8/28 15:47, Mike Rapoport wrote:
>>> On Fri, Aug 25, 2023 at 12:18:35PM +0100, Usama Arif wrote:
>>>> For reserved memory regions marked with this flag,
>>>> reserve_bootmem_region is not called during memmap_init_reserved_pages.
>>>> This can be used to avoid struct page initialization for
>>>> regions which won't need them, for e.g. hugepages with
>>>> HVO enabled.
>>>> 
>>>> Signed-off-by: Usama Arif <usama.arif@...edance.com>
>>>> ---
>>>>  include/linux/memblock.h | 10 ++++++++++
>>>>  mm/memblock.c            | 32 +++++++++++++++++++++++++++-----
>>>>  2 files changed, 37 insertions(+), 5 deletions(-)
>>>> 
>>>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>>>> index f71ff9f0ec81..6d681d053880 100644
>>>> --- a/include/linux/memblock.h
>>>> +++ b/include/linux/memblock.h
>>>> @@ -40,6 +40,8 @@ extern unsigned long long max_possible_pfn;
>>>>   * via a driver, and never indicated in the firmware-provided memory map as
>>>>   * system RAM. This corresponds to IORESOURCE_SYSRAM_DRIVER_MANAGED in the
>>>>   * kernel resource tree.
>>>> + * @MEMBLOCK_RSRV_NOINIT_VMEMMAP: memory region for which struct pages are
>>>> + * not initialized (only for reserved regions).
>>>>   */
>>>>  enum memblock_flags {
>>>>   MEMBLOCK_NONE = 0x0, /* No special request */
>>>> @@ -47,6 +49,8 @@ enum memblock_flags {
>>>>   MEMBLOCK_MIRROR = 0x2, /* mirrored region */
>>>>   MEMBLOCK_NOMAP = 0x4, /* don't add to kernel direct mapping */
>>>>   MEMBLOCK_DRIVER_MANAGED = 0x8, /* always detected via a driver */
>>>> + /* don't initialize struct pages associated with this reserver memory block */
>>>> + MEMBLOCK_RSRV_NOINIT_VMEMMAP = 0x10,
>>> The flag means that struct page shouldn't be initialized, it may be used
>>> not only by vmemmap optimizations.
>>> Please drop _VMEMMAP.
>> 
>> The area at where the struct pages located is vmemmap, I think the
>> "vmemap" suffix does not mean that it is for "vmemmap optimization",
>> it could specify the target which will not be initialized. For me,
>> MEMBLOCK_RSRV_NOINIT does not tell me what should not be initialized,
>> memblock itself or its struct page (aka vmemmap pages)? So maybe
>> the suffix is better to keep?
> In general case the area is memmap rather than vmemmap, so a better suffix

Right. memmap

> then would be _MEMMAP. I'm not too fond of that either, but I cannot think
> of better name.

I have no strong opinion, if we cannot think a better name, just drop the
suffix as you suggested and let the comments more specified. :-)

Thanks.