linux-kernel - Re: [PATCH v8 11/15] khugepaged: allow madvise_collapse to check all anonymous mTHP orders

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Message-ID: <2f6d9541-8083-4d3c-a9c1-cba0d5bf98a0@linux.alibaba.com>
Date: Fri, 4 Jul 2025 14:11:13 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Nico Pache <npache@...hat.com>, linux-mm@...ck.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Cc: david@...hat.com, ziy@...dia.com, lorenzo.stoakes@...cle.com,
 Liam.Howlett@...cle.com, ryan.roberts@....com, dev.jain@....com,
 corbet@....net, rostedt@...dmis.org, mhiramat@...nel.org,
 mathieu.desnoyers@...icios.com, akpm@...ux-foundation.org,
 baohua@...nel.org, willy@...radead.org, peterx@...hat.com,
 wangkefeng.wang@...wei.com, usamaarif642@...il.com, sunnanyong@...wei.com,
 vishal.moola@...il.com, thomas.hellstrom@...ux.intel.com,
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Subject: Re: [PATCH v8 11/15] khugepaged: allow madvise_collapse to check all
 anonymous mTHP orders



On 2025/7/2 13:57, Nico Pache wrote:
> Allow madvise_collapse to scan/collapse all mTHP orders without the
> strict requirement of needing the PMD-order enabled.
> 
> Signed-off-by: Nico Pache <npache@...hat.com>

I am afraid we should drop this patch from the series, since Hugh 
explicitly opposed my modification of the madvise_collapse control logic 
in this thread[1].

Moreover, since we have not yet clarified how to handle the conflict 
between the semantics of madvise_collapse and the THP interfaces, we 
should keep the current logic[2] (means madvise_collapse still only 
allows PMD collapse).

If madvise_collapse is to support mTHP collapse, there will be more 
semantic conflicts to discuss.

[1] 
https://lore.kernel.org/all/cover.1750815384.git.baolin.wang@linux.alibaba.com/
[2] 
https://lore.kernel.org/all/23b8ad10-cd1f-45df-a25c-78d01c8af44f@redhat.com/

> ---
>   mm/khugepaged.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b96a7327b9c0..6ea681b81647 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2930,11 +2930,13 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
>   	unsigned long hstart, hend, addr;
>   	int thps = 0, last_fail = SCAN_FAIL;
>   	bool mmap_locked = true;
> +	unsigned long orders = vma_is_anonymous(vma) ?
> +					THP_ORDERS_ALL_ANON : BIT(PMD_ORDER);
>   
>   	BUG_ON(vma->vm_start > start);
>   	BUG_ON(vma->vm_end < end);
>   
> -	if (!thp_vma_allowable_order(vma, vma->vm_flags, 0, PMD_ORDER))
> +	if (!thp_vma_allowable_orders(vma, vma->vm_flags, 0, orders))
>   		return -EINVAL;
>   
>   	cc = kmalloc(sizeof(*cc), GFP_KERNEL);
> @@ -2956,7 +2958,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
>   			mmap_read_lock(mm);
>   			mmap_locked = true;
>   			result = hugepage_vma_revalidate(mm, addr, false, &vma,
> -							 cc, BIT(HPAGE_PMD_ORDER));
> +							 cc, orders);
>   			if (result  != SCAN_SUCCEED) {
>   				last_fail = result;
>   				goto out_nolock;