linux-kernel - Re: [PATCH] kho: simplify page initialization in kho_restore

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Message-ID: <868qel9fje.fsf@kernel.org>
Date: Mon, 29 Dec 2025 21:52:37 +0100
From: Pratyush Yadav <pratyush@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: Pratyush Yadav <pratyush@...nel.org>,  Andrew Morton
 <akpm@...ux-foundation.org>,  Alexander Graf <graf@...zon.com>,  Mike
 Rapoport <rppt@...nel.org>,  kexec@...ts.infradead.org,
  linux-mm@...ck.org,  linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kho: simplify page initialization in kho_restore_page()

On Tue, Dec 23 2025, Pasha Tatashin wrote:

> On Tue, Dec 23, 2025 at 5:45 AM Pratyush Yadav <pratyush@...nel.org> wrote:
>>
>> When restoring a page (from kho_restore_pages()) or folio (from
>> kho_restore_folio()), KHO must initialize the struct page. The
>> initialization differs slightly depending on if a folio is requested or
>> a set of 0-order pages is requested.
>>
>> Conceptually, it is quite simple to understand. When restoring 0-order
>> pages, each page gets a refcount of 1 and that's it. When restoring a
>> folio, head page gets a refcount of 1 and tail pages get 0.
>>
>> kho_restore_page() tries to combine the two separate initialization flow
>> into one piece of code. While it works fine, it is more complicated to
>> read than it needs to be. Make the code simpler by splitting the two
>> initalization paths into two separate functions. This improves
>> readability by clearly showing how each type must be initialized.
>>
>> Signed-off-by: Pratyush Yadav <pratyush@...nel.org>
>> ---
>>
>> Notes:
>>     This patch is a follow up from
>>     https://lore.kernel.org/linux-mm/86ms42mj44.fsf@kernel.org/
>>
>>  kernel/liveupdate/kexec_handover.c | 41 ++++++++++++++++++++----------
>>  1 file changed, 27 insertions(+), 14 deletions(-)
>>
>> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
>> index 2d9ce33c63dc..304c26fd5ee6 100644
>> --- a/kernel/liveupdate/kexec_handover.c
>> +++ b/kernel/liveupdate/kexec_handover.c
>> @@ -219,11 +219,33 @@ static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn,
>>         return 0;
>>  }
>>
>> +/* For physically contiguous 0-order pages. */
>> +static void kho_init_pages(struct page *page, unsigned int nr_pages)
>
> Here and in other places below, it is better for nr_pages to be
> unsigned long. This is consistent with other places in mm, where we
> have gradually moved on from int/unsigned int to unsigned long for
> npages (see gup.c for example). Otherwise, LGTM.

Thanks. Will do.

[...]

-- 
Regards,
Pratyush Yadav