linux-kernel - Re: [PATCH RESEND v2 5/6] mm/page_alloc: forward the gfp flags from alloc_contig_range() to post_alloc

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Message-ID: <d7b7a5c7-ef3f-44f2-9eb6-817b21ffc00e@suse.cz>
Date: Tue, 3 Dec 2024 15:36:55 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
 Andrew Morton <akpm@...ux-foundation.org>, Oscar Salvador
 <osalvador@...e.de>, Zi Yan <ziy@...dia.com>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Naveen N Rao <naveen@...nel.org>, Madhavan Srinivasan <maddy@...ux.ibm.com>
Subject: Re: [PATCH RESEND v2 5/6] mm/page_alloc: forward the gfp flags from
 alloc_contig_range() to post_alloc_hook()

On 12/3/24 10:47, David Hildenbrand wrote:
> In the __GFP_COMP case, we already pass the gfp_flags to
> prep_new_page()->post_alloc_hook(). However, in the !__GFP_COMP case, we
> essentially pass only hardcoded __GFP_MOVABLE to post_alloc_hook(),
> preventing some action modifiers from being effective..
> 
> Let's pass our now properly adjusted gfp flags there as well.
> 
> This way, we can now support __GFP_ZERO for alloc_contig_*().
> 
> As a side effect, we now also support __GFP_SKIP_ZERO and__GFP_ZEROTAGS;
> but we'll keep the more special stuff (KASAN, NOLOCKDEP) disabled for
> now.
> 
> It's worth noting that with __GFP_ZERO, we might unnecessarily zero pages
> when we have to release part of our range using free_contig_range() again.
> This can be optimized in the future, if ever required; the caller we'll
> be converting (powernv/memtrace) next won't trigger this.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/page_alloc.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 54594cc4f650..71d70bc0ad79 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6364,7 +6364,7 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
>  	return (ret < 0) ? ret : 0;
>  }
>  
> -static void split_free_pages(struct list_head *list)
> +static void split_free_pages(struct list_head *list, gfp_t gfp_mask)
>  {
>  	int order;
>  
> @@ -6375,7 +6375,7 @@ static void split_free_pages(struct list_head *list)
>  		list_for_each_entry_safe(page, next, &list[order], lru) {
>  			int i;
>  
> -			post_alloc_hook(page, order, __GFP_MOVABLE);
> +			post_alloc_hook(page, order, gfp_mask);
>  			set_page_refcounted(page);
>  			if (!order)
>  				continue;
> @@ -6393,7 +6393,8 @@ static void split_free_pages(struct list_head *list)
>  static int __alloc_contig_verify_gfp_mask(gfp_t gfp_mask, gfp_t *gfp_cc_mask)
>  {
>  	const gfp_t reclaim_mask = __GFP_IO | __GFP_FS | __GFP_RECLAIM;
> -	const gfp_t action_mask = __GFP_COMP | __GFP_RETRY_MAYFAIL | __GFP_NOWARN;
> +	const gfp_t action_mask = __GFP_COMP | __GFP_RETRY_MAYFAIL | __GFP_NOWARN |
> +				  __GFP_ZERO | __GFP_ZEROTAGS | __GFP_SKIP_ZERO;
>  	const gfp_t cc_action_mask = __GFP_RETRY_MAYFAIL | __GFP_NOWARN;
>  
>  	/*
> @@ -6541,7 +6542,7 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
>  	}
>  
>  	if (!(gfp_mask & __GFP_COMP)) {
> -		split_free_pages(cc.freepages);
> +		split_free_pages(cc.freepages, gfp_mask);
>  
>  		/* Free head and tail (if any) */
>  		if (start != outer_start)