linux-kernel - Re: [PATCH v3 4/6] mm: Introduce a pageflag for partially mapped folios

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Message-Id: <20240815163013.2522e3dd83acffe70af9cba6@linux-foundation.org>
Date: Thu, 15 Aug 2024 16:30:13 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Usama Arif <usamaarif642@...il.com>
Cc: Barry Song <21cnbao@...il.com>, baohua@...nel.org,
 cerasuolodomenico@...il.com, corbet@....net, david@...hat.com,
 hannes@...xchg.org, kernel-team@...a.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, riel@...riel.com,
 roman.gushchin@...ux.dev, rppt@...nel.org, ryan.roberts@....com,
 shakeel.butt@...ux.dev, willy@...radead.org, yuzhao@...gle.com
Subject: Re: [PATCH v3 4/6] mm: Introduce a pageflag for partially mapped
 folios

On Thu, 15 Aug 2024 16:25:09 +0100 Usama Arif <usamaarif642@...il.com> wrote:

> 
> 
> commit c627655548fa09b59849e942da4decc84fa0b0f2
> Author: Usama Arif <usamaarif642@...il.com>
> Date:   Thu Aug 15 16:07:20 2024 +0100
> 
>     mm: Introduce a pageflag for partially mapped folios fix
>     
>     Fixes the original commit by not clearing partially mapped bit
>     in hugeTLB folios and fixing deferred split THP stats.
>
> ...
>

Life is getting complicated.

> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1758,7 +1758,6 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
>                 free_gigantic_folio(folio, huge_page_order(h));
>         } else {
>                 INIT_LIST_HEAD(&folio->_deferred_list);
> -               folio_clear_partially_mapped(folio);
>                 folio_put(folio);
>         }
>  }

Yu Zhao's "mm/hugetlb: use __GFP_COMP for gigantic folios" was
expecting that folio_clear_partially_mapped() to be there.

I resolved this within
mm-hugetlb-use-__gfp_comp-for-gigantic-folios.patch thusly:

@@ -1748,18 +1704,8 @@ static void __update_and_free_hugetlb_fo
 
 	folio_ref_unfreeze(folio, 1);
 
-	/*
-	 * Non-gigantic pages demoted from CMA allocated gigantic pages
-	 * need to be given back to CMA in free_gigantic_folio.
-	 */
-	if (hstate_is_gigantic(h) ||
-	    hugetlb_cma_folio(folio, huge_page_order(h))) {
-		destroy_compound_gigantic_folio(folio, huge_page_order(h));
-		free_gigantic_folio(folio, huge_page_order(h));
-	} else {
-		INIT_LIST_HEAD(&folio->_deferred_list);
-		folio_put(folio);
-	}
+	INIT_LIST_HEAD(&folio->_deferred_list);
+	hugetlb_free_folio(folio);
 }
 
 /*

Please check.