linux-kernel - Re: [PATCH 2/3] mm: hugetlb: make the hugetlb migration strategy consistent

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Date: Wed, 6 Mar 2024 16:58:23 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Oscar Salvador <osalvador@...e.de>
Cc: akpm@...ux-foundation.org, muchun.song@...ux.dev, david@...hat.com,
 linmiaohe@...wei.com, naoya.horiguchi@....com, mhocko@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm: hugetlb: make the hugetlb migration strategy
 consistent



On 2024/3/6 16:46, Oscar Salvador wrote:
> On Wed, Mar 06, 2024 at 04:35:26PM +0800, Baolin Wang wrote:
>> On 2024/2/28 16:41, Oscar Salvador wrote:
> 
>>>    	if (folio_test_hugetlb(src)) {
>>>    		struct hstate *h = folio_hstate(src);
>>> +		bool allow_fallback = false;
>>> +
>>> +		if ((1UL << reason) & HTLB_ALLOW_FALLBACK)
>>> +			allow_fallback = true;
>>
>> IMHO, users also should not be aware of these hugetlb logics.
> 
> Note that what I wrote there was ugly, because it was just a PoC.
> 
> It could be a helper e.g:
> 
>   if (hugetlb_reason_allow_alloc_fallback(reason)) (or whatever)
>       allow_fallback_alloc = true
> 
>>>
>>>    		gfp_mask = htlb_modify_alloc_mask(h, gfp_mask);
>>>    		return alloc_hugetlb_folio_nodemask(h, nid,
>>> -						mtc->nmask, gfp_mask);
>>> +						mtc->nmask, gfp_mask,
>>> +						allow_fallback);
>>
>> 'allow_fallback' can be confusing, that means it is 'allow_fallback' for a
>> new temporary hugetlb allocation, but not 'allow_fallback' for an available
>> hugetlb allocation in alloc_hugetlb_folio_nodemask().
> 
> Well, you can pick "alloc_fallback_on_alloc" which is more descriptive I
> guess.

Seems better.

> 
> Bottomline line is that I do not think that choosing to allow
> fallbacking or not here is spreading more logic than having the
> htlb_modify_alloc_mask() here and not directly in
> alloc_hugetlb_folio_nodemask().
> 
> As I said, code-wise looks fine, it is just that having to pass
> the 'reason' all the way down and making the decision there makes
> me go "meh..".

Well, fair enough:) let me respin it. Thanks.