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[99.79.140.187]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ada4896c4dsm1605274a91.7.2026.10.21.17.53.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Oct 2026 17:53:16 -0700 (PDT) From: Zhijian Han To: Kiryl Shutsemau Cc: Andrew Morton , David Hildenbrand , Nico Pache , Baolin Wang , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: khugepaged selftest: intermittent collapse_full(madvise:anon) failure and low-memory false failures on arm64 64K Date: Thu, 22 Oct 2026 08:53:03 +0800 Message-ID: <20261022005303.750032-1-hanzhijian1991@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261020024116.2949892-1-hanzhijian1991@gmail.com> References: <20261020024116.2949892-1-hanzhijian1991@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Kiryl, Thanks — instrumented as suggested: errno + thp_collapse_alloc_failed printed on failure, then 30 full runs on the same setup (QEMU arm64 64K, 6G, linux-next 20261019). The failure reproduced 11/30 times and the data does not point at allocation: 6x EAGAIN, 5x EINVAL, 0x ENOMEM thp_collapse_alloc_failed=0 in every failing run Per madvise_collapse_errno(), EAGAIN maps to transient page states (SCAN_PAGE_LOCK/PAGE_LRU/PAGE_DIRTY_OR_WRITEBACK/...) and EINVAL to "intrinsic" scan results — neither is the allocation-failure path, which would have shown ENOMEM and a bump in the counter. One thing that stands out: madvise_collapse_retry() retries EAGAIN only once, so two consecutive EAGAINs fail the case even though the errno table documents EAGAIN as "trying again might succeed". Could the test retry harder on EAGAIN (loop with a short sleep), or is the single retry deliberate to expose genuine kernel-side transients? For the EINVAL cases I would need kernel-side detail on which scan result is being hit; happy to run instrumented (tracefs or a debug counter) if you point me at the right knob. Full 30-run logs and the instrumentation diff available on request. Understood and agreed on the low-memory guard — dropped. Assisted-by: LLM (QEMU test harness and instrumentation) -- Zhijian Han