linux-kernel - Re: [RFC PATCH 02/12] khugepaged: Generalize alloc_charge

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Message-ID: <Z2D7YctQaFW_iwei@casper.infradead.org>
Date: Tue, 17 Dec 2024 04:17:37 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, david@...hat.com,
	kirill.shutemov@...ux.intel.com, ryan.roberts@....com,
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	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 02/12] khugepaged: Generalize alloc_charge_folio()

On Mon, Dec 16, 2024 at 10:20:55PM +0530, Dev Jain wrote:
>  static int alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
> -			      struct collapse_control *cc)
> +			      int order, struct collapse_control *cc)

unsigned, surely?

>  	if (!folio) {
>  		*foliop = NULL;
>  		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
> +		if (order != HPAGE_PMD_ORDER)
> +			count_mthp_stat(order, MTHP_STAT_ANON_COLLAPSE_ALLOC_FAILED);

i don't understand why we need new statistics here.  we already have a
signal that memory allocation failures are preventing collapse from
being successful, why do we care if it's mthp or actual thp?

>  	count_vm_event(THP_COLLAPSE_ALLOC);
> +	if (order != HPAGE_PMD_ORDER)
> +		count_mthp_stat(order, MTHP_STAT_ANON_COLLAPSE_ALLOC);

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