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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93c248e22f7sm310457085a.47.2026.09.23.14.33.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Sep 2026 14:33:56 -0700 (PDT) Date: Wed, 23 Sep 2026 17:33:53 -0400 From: Gregory Price To: Yeoreum Yun Cc: Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , Shuah Khan Subject: Re: [PATCH v3 2/2] kselftest: mm: fix intermittent failure khugepaged test Message-ID: References: <20260923-fix_khugepagd_fail-v3-0-b387e92fe1a9@arm.com> <20260923-fix_khugepagd_fail-v3-2-b387e92fe1a9@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260923-fix_khugepagd_fail-v3-2-b387e92fe1a9@arm.com> X-Rspam-User: X-Stat-Signature: 9xnbuu5dtmnqh4yptwuj4cyg3os7qobt X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 7B30810000D X-HE-Tag: 1790199237-394828 X-HE-Meta: U2FsdGVkX19JXF8uB1o2bMRI0oxzVn+z4481yHd/MAWc7eQ3kv4jza98IFFgB7uADYGQIONBXoj1q6QDkxD1DTbg3XuMEDn6p31ZVF1HxCTagOsDQsI6mHMliOmyplov/w0RhjUDSDbFbVSjoY6XikI0c5+1OY31EGAfFrLdXpjp3Te/m/nM/FMF5Oup7Qmwgqk7C/IjR1jnGCiKiGG+o7Ya8yU8N20Vphllqp5RVcySYKa/G5YGYEI0ywI4fbAvMfwhfA7TAdtX7V22zYImGoq0KyUQUMmLcBycB5Oayeh0FVYkPMXaMJ8+lkAyDII2PRN5KlNVxa66gDbbEaMXJrAGkBuOiQaoWUHFdbhQF4INvSTZslgbXvXcPm25B7HrmgTSLZRNy5F3BRmqOUiLxoWt9D9av6SWBhplZlupIUmEov0l0Sw+BHTyFHD3FQUjhVZ9EMemW3l7/Zzrb0S/IOr1fIq0qCmVhpiA+h3pc0NPaBPQH4qWgLPo9vPFWYxtQuB1ZHLLTt3oiM7JIK+6EWuWJWAAcc0B2DsOe4K1hnrRETS1WnVwB8dIik65Dis7BeDQe+dvRM0qTTdU7m4bqN41TJhBSPMr5sr/L75FlGeSnyWIBEgZWmiicigbVKXx5MEKgDTHyR5CekQ2NsGmOS4ysuXtFJtZ11bTfnNOuoRlgm7uDZHgTaQfJGIOwuVvxTCo7mI7FJAc1tR39LyAre2bicoSWo9bemFgBOcEXECjcFlmiAuJJ9yteRRTytOPVZj9mux3r3PPHVpg2OGyaW9Rhzh36pjytUFiBkZYCzri+Mg/FHRDC5sJ9pFvKgclfjcjpef6Ajj5je4N+nklwDQq6HG2E/dnBjhERxnuFeUv2RD8kOzPB/DD4zVQa4z8wvUWg7NyQz0t/SlrGofc/vmXxfNiI19eb2IUmY+imISh+6BZ7ufkAh5peRSyzVC/LFBwfOVTgGgdYtOcHgd pBsd8pDS iuF74vQIobRcRQSWnx0mhJ3J+80RzHeCaaYZa0f76IJoRihL5c6iHXuqTlynyzbl+DEg9DIcIX7gIZ5GXFCkqkCWi68T5vN7zkZSrO+HJo1cm0Y7BvF0KS+tW5cqe6OzOU894przMVyMZWoLJklUibzIO6RYehidvU6Cw32GRPfM10j9gdsTJNXmWT1fga6EHGFjqCJtb2rhpK/xARK6OCqE/GcUI02bwdNHXfKzO9GsWKO8tOVj4Wx2hmFsKt8OVQDfngic5a/zsJyu3gOlodG3PnVabZ3x7L3TCNRSPD/mIeFohJdg6syjis1v2Gg0PtQGK78ycRgnVSoXcKjSQpKK9HuwT5zDb6ejpfYQb6OtsEhesXfHWjHi21Ks7BlyV7xTOdlBhf9YcgBAV7Pje8tP09faicO9PK1ZmTCNfHgvKA64O2Tk665Vm8YD7bwELYNHbjlalGl7L1V5ffyQBkJQ3pw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 23, 2026 at 04:29:52PM +0100, Yeoreum Yun wrote: > There are intermittent failures in collapse_max_ptes_swap() and > collapse_max_ptes_shared() when using the khugepaged_context: > > // while running ./khugepaged -s 2 > > # Run test: collapse_max_ptes_shared (khugepaged:anon) > # Allocate huge page... OK > # Share huge page over fork()... OK > # Trigger CoW on page 1023 of 2048... OK > # Maybe collapse with max_ptes_shared exceeded.... OK > # Trigger CoW on page 1024 of 2048... Fail > Bail out! Unexpected huge page > # Planned tests != run tests (26 != 23) > # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0 > > # Run test: collapse_max_ptes_swap (khugepaged:anon) > # Swapout 257 of 2048 pages... OK > # Maybe collapse with max_ptes_swap exceeded.... OK > # Swapout 256 of 2048 pages... OK > Bail out! Unexpected huge page > # Planned tests != run tests (26 != 17) > # Totals: pass:17 fail:0 xfail:0 xpass:0 skip:0 error:0 > > This happens because khugepaged may collapse the pages before wait_for_scan() > is called, causing a sanity check that expects uncollapsed pages to fail. > > For example, in collapse_max_ptes_swap(), after faulting the pages back in > and paging out up to max_ptes_swap pages, khugepaged may collapse them again > before c->collapse() is called. > > To prevent this, mark the VMA with MADV_NOHUGEPAGE after it has been > collapsed by wait_for_scan() for anon. This prevents khugepaged from > collapsing it again before c->collapse() is called. > > This failure was observed on NVIDIA Spark with 16KB page. > > Reviewed-by: Baolin Wang > Tested-by: Baolin Wang > Signed-off-by: Yeoreum Yun Reviewed-by: Gregory Price (Meta)