linux-kernel - Re: [PATCH v5 3/4] mm: thp: use folio_batch to handle THP splitting in deferred_split

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Message-Id: <20251106182949.1ffd6f5529aa18139f2ba9f3@linux-foundation.org>
Date: Thu, 6 Nov 2025 18:29:49 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Wei Yang <richard.weiyang@...il.com>
Cc: Qi Zheng <qi.zheng@...ux.dev>, hannes@...xchg.org, hughd@...gle.com,
 mhocko@...e.com, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
 muchun.song@...ux.dev, david@...hat.com, lorenzo.stoakes@...cle.com,
 ziy@...dia.com, harry.yoo@...cle.com, baolin.wang@...ux.alibaba.com,
 Liam.Howlett@...cle.com, npache@...hat.com, ryan.roberts@....com,
 dev.jain@....com, baohua@...nel.org, lance.yang@...ux.dev,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
 Muchun Song <songmuchun@...edance.com>, Qi Zheng
 <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v5 3/4] mm: thp: use folio_batch to handle THP splitting
 in deferred_split_scan()

On Thu, 6 Nov 2025 14:52:13 +0000 Wei Yang <richard.weiyang@...il.com> wrote:

> >+		if (folio_order(folio) > 1) {
> >+			if (!list_empty(&folio->_deferred_list)) {
> >+				ds_queue->split_queue_len--;
> >+				/*
> >+				 * Reinitialize page_deferred_list after removing the
> >+				 * page from the split_queue, otherwise a subsequent
> >+				 * split will see list corruption when checking the
> >+				 * page_deferred_list.
> >+				 */
> >+				list_del_init(&folio->_deferred_list);
> >+			}
> > 			if (folio_test_partially_mapped(folio)) {
> > 				folio_clear_partially_mapped(folio);
> > 				mod_mthp_stat(folio_order(folio),
> > 					      MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, -1);
> > 			}
> >-			/*
> >-			 * Reinitialize page_deferred_list after removing the
> >-			 * page from the split_queue, otherwise a subsequent
> >-			 * split will see list corruption when checking the
> >-			 * page_deferred_list.
> >-			 */
> >-			list_del_init(&folio->_deferred_list);
> 
> @Andrew
> 
> Current mm-new looks not merge the code correctly?
> 

It happens.  We presently have 29 patches which alter mm/huge_memory.c.

Thanks for checking.  I'll drop version 5 of "reparent the THP split queue".

Please check what remains, and send a v6 against tomorrow's
mm-new/mm-unstable.