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Howlett" , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Shuah Khan Subject: [PATCH v2 4/7] mm/khugepaged: fix outdated comments Date: Tue, 14 Jul 2026 20:59:33 -0600 Message-ID: <20260715025941.1571316-5-npache@redhat.com> In-Reply-To: <20260715025941.1571316-1-npache@redhat.com> References: <20260715025941.1571316-1-npache@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-Mimecast-MFC-PROC-ID: t91916uA0r1QTWx9jZ8-wPtvBsEk5tlwZ9AnlVaOXOM_1784084449 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 31A8220010 X-Stat-Signature: k6n6stbpgw3igii57r53oji95m4y6yte X-HE-Tag: 1784084457-26648 X-HE-Meta: U2FsdGVkX1/Z1Mm6wK2Q1JDreId9BPe/i1T/R6rPXKWhZ3K/LV2SzbppsYUJklF5tG0jNlbUUtD6FFYJjg2LEZNwcIzilLF5ynycOA/Rd3ecKXsVDduxaxInAeMU61MWqWHoSgUEODesLgK52lFvufj8pn2FTG0M8mW+s43ipA0/9O2dkzJulZWpz/YkSHMWMelGNSrox72gMnGEdzvsXt3RRww4q+/dJTVzVRvFZClFErXMvSRggZDomfkPDbcX7AJjxPZOqKmXuYGPCCml3a0DE/NRzQR2s5BLJfNerjOqWxf9pSSv1ks09lHyJsXcnTYPfMGTtdZhOzMJrCfO1eHbu4+//PWO28gCxJUa/rrwUa+lZNZZzyva2vbxOL+sKrn39bZq+k6I+EVBntQJZoTWpP8CkO0PQ0hCEc7rVW9qdyJx5EDyZ9o9FopyZkKfGqs50/P5YCenF4NQzpVG9koeiJ2pcR8rN7XxKxlpYQwm84M6uAxZ4yda1joEr8XWY22kiDKRXC7aZ94o3EuSIOv1ovH//oQnVWo3TbqX4tg3u7GlX7DZUQQ9Tijdb3tx6s04/NVVa6GPJnHlKyL3FR9wsl2998WcKnaS+6OZMfVwgIYDtjTcU4vzdc1xtaG2QDU9cdaPxOobOc5gL+z9/X5lLWBNK+uzovwNDX1nXGWTsRageZnxlE5UsxC0ki+gDmNq7Y6HCdui4q7siQ7iKCKOcFemmg+T2IauFdqQOVN0utkFZ+Cc+hjQ7YMnqqWslin/1cfbna77wJZi0EcqOOUQ/FIC+JPESWJq/I8dzhU7g/2ZQtWTRWZuYLYNRIy9e5bGnQpcvogG6io8edeGjc9ffwZk77L1cgbZe//mpWrfoSt7QmIiui0hd4VV5IbLtlN4mE7jjXIr6OIFA9rnYVV85N2EaOjtVuEW6lclZe+D6xUDZd0bNIOVMZSsDfDMWy5zR6RVQ/XxFbvCV0v fi7Q34v0 xExyv06fXT52Bx9TngkQu/vxgWDC27VF6XQ3qZbXXjBCooLlOiuOqc7p5L8egrjQ5X5+Pb81Q96gfn9af5ELdff+9QS2JJViumFIHUhXFfujO5Rlch/TT2siUx1/Ni9X6RKSBawbwOjPVM8J2FmxtyUsOXHXMxu97Iwecm+XLL7ydLLzDjvdr+uSmRxWLcpOM4S3547PsZLdlNIaiu8Hf0w9V4Q1zi6U9n5P78x4FW5OOsuf/Rw0Oy0XMRdzaCXhffKY2WVU9gWzbXS4nxh2Y6JJfUsxI+aTzgRtf7BlBeBhU/4iPYjRSCuYLlN903ypSP2YPh0y6UakLFWxNPsf6BNMxYQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Fix comment in collapse_scan_pmd() that still described the old folio_mapcount() > folio_ref_count() check and a "512" false-positive scenario. The code now uses folio_expected_ref_count() != folio_ref_count() which doesn't suffer from the same limitation. Fix comment in collapse_huge_page() that referenced ptep_clear_flush, when the code actually uses pmdp_collapse_flush. Fix comment in __collapse_huge_page_swapin() that referenced the old function name khugepaged_scan_pmd, now collapse_scan_pmd. Also clean up some simple typos and stale terminology (mmap_sem -> mmap_lock, PG_lock -> folio lock, page -> folio, grammar). We also clarify a comment regarding where the max_ptes_none check is deferred to in mthp_collapse() from the original collapse_scan_pmd check. Acked-by: Usama Arif Assisted-by: Cursor(claude-sonnet-4):4.6 Signed-off-by: Nico Pache --- mm/khugepaged.c | 26 ++++++++++++-------------- 1 file changed, 12 insertions(+), 14 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index f65bbe2051b3..d785468ffb96 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -620,7 +620,7 @@ void __khugepaged_exit(struct mm_struct *mm) /* * This is required to serialize against * collapse_test_exit() (which is guaranteed to run - * under mmap sem read mode). Stop here (after we return all + * under mmap_lock read mode). Stop here (after we return all * pagetables will be destroyed) until khugepaged has finished * working on the pagetables under the mmap_lock. */ @@ -789,7 +789,7 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, /* * We can do it before folio_isolate_lru because the - * folio can't be freed from under us. NOTE: PG_lock + * folio can't be freed from under us. NOTE: folio lock * is needed to serialize against split_huge_page * when invoked from the VM. */ @@ -816,7 +816,7 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, } /* - * Isolate the page to avoid collapsing an hugepage + * Isolate the folio to avoid collapsing a hugepage * currently in use by the VM. */ if (!folio_isolate_lru(folio)) { @@ -1101,7 +1101,7 @@ static enum scan_result hugepage_vma_revalidate(struct mm_struct *mm, unsigned l return SCAN_VMA_CHECK; /* * Anon VMA expected, the address may be unmapped then - * remapped to file after khugepaged reaquired the mmap_lock. + * remapped to file after khugepaged reacquired the mmap_lock. * * thp_vma_allowable_orders may return true for qualified file * vmas. @@ -1159,7 +1159,7 @@ static enum scan_result check_pmd_still_valid(struct mm_struct *mm, /* * Bring missing pages in from swap, to complete THP collapse. - * Only done if khugepaged_scan_pmd believes it is worthwhile. + * Only done if collapse_scan_pmd believes it is worthwhile. * * For mTHP orders the function bails on the first swap entry, because * faulting pages back in during collapse could re-populate PTEs that @@ -1351,8 +1351,8 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long s mmap_read_unlock(mm); /* * Prevent all access to pagetables with the exception of - * gup_fast later handled by the ptep_clear_flush and the VM - * handled by the anon_vma lock + PG_lock. + * gup_fast later handled by the pmdp_collapse_flush and the VM + * handled by the anon_vma lock + folio lock. * * UFFDIO_MOVE is prevented to race as well thanks to the * mmap_lock. @@ -1643,7 +1643,8 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, /* * If PMD is the only enabled order, enforce max_ptes_none, otherwise - * scan all pages to populate the bitmap for mTHP collapse. + * scan all pages to populate the bitmap for mTHP collapse. The bitmap + * is then checked again in mthp_collapse() for each attempted order. */ if (enabled_orders != BIT(HPAGE_PMD_ORDER)) max_ptes_none = KHUGEPAGED_MAX_PTES_LIMIT; @@ -1764,12 +1765,9 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, /* * Check if the page has any GUP (or other external) pins. * - * Here the check may be racy: - * it may see folio_mapcount() > folio_ref_count(). - * But such case is ephemeral we could always retry collapse - * later. However it may report false positive if the page - * has excessive GUP pins (i.e. 512). Anyway the same check - * will be done again later the risk seems low. + * Here the check is racy, but such case is ephemeral and + * we could always retry collapse later. Anyway the same + * check will be done again later the risk seems low. */ if (folio_expected_ref_count(folio) != folio_ref_count(folio)) { result = SCAN_PAGE_COUNT; -- 2.54.0