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From: "Kunwu Chan" Message-ID: <4915dbdd42711403f1781e3c7a71a11a53b0249d@linux.dev> TLS-Required: No Subject: Re: [PATCH 4/5] selftests/damon/damos_tried_regions: handle empty tried regions in early cycles To: "SeongJae Park" Cc: "SeongJae Park" , shuah@kernel.org, damon@lists.linux.dev, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, "Kunwu Chan" , "Wang Lian" , "Kunwu Chan" In-Reply-To: <20260531165437.99410-1-sj@kernel.org> References: <20260531165437.99410-1-sj@kernel.org> X-Migadu-Flow: FLOW_OUT X-Stat-Signature: cnc3b64e4spmnitjph4hx5pkkkkzk6w5 X-Rspamd-Queue-Id: CBAE480006 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1780281238-707625 X-HE-Meta: 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 /6RLeDoq /4VmsPmt0b36oToT7uBHRIXQr+1cE70f/UrjXyOKbggnje6d9BNlJIfoAMvU5X7tUZP1gY6jjut77MdDMFBC2q80cgFXopXSk1LszFNy4ZSl8UFID+nJ4I/FWPZWUbheLp6vgHcCa8b6JVxhZmJOehiCHM9BTg8nbdeHLs2f79uAovxKGRpymDs1LhcWyy515SgnrQxCZk2ktEFjbUNXrd9Y5BNm0bgavzR70BUsHUlgUxadAv4ZigVrthVI29x90dBKqVZFygVIjbwTpyYKhSAhcFhOiWuZIyHpEKrq1dLXpnEoR1yyUouUThE9D0awENlMUTaxAcFj6L8p24yqp+DQS/qxEGT09KdH+dCb7RjYiN8T9t18ZOJXPUA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: June 1, 2026 at 12:54 AM, "SeongJae Park" wrote: >=20 >=20On Sun, 31 May 2026 17:17:23 +0800 Kunwu Chan = wrote: >=20 >=20>=20 >=20> From: Kunwu Chan > >=20=20 >=20> The test aborts if the initial aggregation cycles produce zero > > tried regions. This can happen on slow machines, causing false > > failures. Skip empty cycles and retry up to 200 times before > > giving up. Also check that enough samples were collected before > > computing the 50th percentile. > >=20 >=20I agree this will make the test be more reliable. I'm bit concerned i= f 200 > times retry can make the test run too long, though. >=20 >=20Also, could you further elaborate why this can fail on slow machines?= That is, > DAMON will check the access of 'access_memory_even' process every 5ms. = Are you > thinking the 5ms is too short for 'access_memory_event' to make the exp= ected > access (accessing the 7 regins of 10 MiB size) within? If so, should we > increase the sampling interval before retrying? >=20 >=20I also suspect if the unreliable results you seen is due to the fact = that DAMON > is not flushing TLB, like we discussed before. If that's the case, coul= d we > increase the working set size of this test, similar to the wss_estimati= on test? >=20 Thanks,=20SJ. Good points. I don't yet have enough evidence to say whether this is primarily due to scheduling delays, a too-short sampling interval, or effects from not flushing TLB. I'll investigate the root cause and see if increasing the working set size or adjusting the test configuration may be a cleaner solution than adding retries. I'll drop this patch from v2 for now and revisit it once I better understand the root cause. Thanks, Kunwu > [1] https://lore.kernel.org/20260525144846.604907-1-kunwu.chan@linux.de= v >=20 >=20Thanks, > SJ >=20 >=20[...] >