linux-kernel - Re: [PATCH 1/5] mm/compaction: allow blockpfn outside of pageblock for high order buddy page

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Date:   Tue, 1 Aug 2023 12:12:03 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kemeng Shi <shikemeng@...weicloud.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        baolin.wang@...ux.alibaba.com, mgorman@...hsingularity.net,
        willy@...radead.org, david@...hat.com
Subject: Re: [PATCH 1/5] mm/compaction: allow blockpfn outside of pageblock
 for high order buddy page

On Sun, 30 Jul 2023 01:43:50 +0800 Kemeng Shi <shikemeng@...weicloud.com> wrote:

> Commit 9fcd6d2e052ee ("mm, compaction: skip compound pages by order in
> free scanner") skiped compound pages to save iterations and limit blockpfn
> to reach outside of page block in case of bogus compound_order. While this
> also limit pfnblock outside page block in case a buddy page with order
> higher than page block is found. After this, isolate_freepages_range will
> fail unexpectedly as it will fail to isolate the page block which was
> isolated successfully by high order buddy page in previous page block
> and abort the free page isolation.
> 
> Fix this by allow blockpfn outside of pageblock in case of high order
> buddy page.
> 
> ...
>
> @@ -1418,7 +1420,7 @@ fast_isolate_around(struct compact_control *cc, unsigned long pfn)
>  	isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
>  
>  	/* Skip this pageblock in the future as it's full or nearly full */
> -	if (start_pfn == end_pfn && !cc->no_set_skip_hint)
> +	if (start_pfn >= end_pfn && !cc->no_set_skip_hint)
>  		set_pageblock_skip(page);
>  }
>  

This needed alteration for mm-unstable changes:

@@ -1441,7 +1443,7 @@ fast_isolate_around(struct compact_contr
 	isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
 
 	/* Skip this pageblock in the future as it's full or nearly full */
-	if (start_pfn == end_pfn)
+	if (start_pfn >= end_pfn)
 		set_pageblock_skip(page);
 
 	return;