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b=J6X95oTbOAS3XyTF0Dmt6wrD17Kvgl97r+sYxRrN3bzDEaNkg+d2uLZfGFngtgb9a rahioNH2tDN2hSjLgrp49QPC5chnLUOXdclMlOl3EjWCR6AJ4JG0XcB9mtn2e63AaN 9G47GhDisB6kb4+bOH4cqao/EDJW6bTWRbh6H8QZ9S8Nc7AhbFEnaQGr3V8e5fn+2E PrLcdPKyHMukj0XKaa2J57USMBGYr/JI4xH9Rrja6wYCd89g0p/ZiJfo/rOnyacf4U HpW0xB1QdECfsjlYxYkgro8hIeY7IBCaw18ZNWPUzB28ARfFk8X6wf8Bf33aTzR7/m 2LxJ5v/6Im24g== From: SeongJae Park To: SeongJae Park Cc: Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: (sashiko review) [PATCH] mm/damon/core: disallow non-power of two min_region_sz on damon_start() Date: Sat, 11 Apr 2026 16:34:30 -0700 Message-ID: <20260411233431.78220-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260411213638.77768-1-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: DEACA4000B X-Stat-Signature: rugkzmt73rspg75ge4qeh5h7kkbpxbk8 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1775950479-675542 X-HE-Meta: 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 1KvMfQZE +gYLPNO+q7SB0VFlR1ZaAEMbQp3sJR4t//rBF0PIJ5epfS5DoEiYgc6R2mkbloNdc/3vS4InvE+8kvn0dEcTGjkGluqyliTnHI4ttt0krUMRshjVN2t6Hwd7/8IXvtAUez8H2PLHFz8NKurZVt4nPbsDfOPchYyPU7/wL+CMw7jNmgCSHiDm9tuD17pavDv8DjlQf4dkHsMA/x+R+//y5eIMrXCjhxo194vf+9QIT1Bko4JM4wrFUzPGq0og9ATMc/Oz5XYWrFvy7Fdn9/fQRXnepvZ+sU7zoqoH1uQMscmXHkjUD7mF5fo+yWlIrnNFXCW6qLf1cw/YeIQD7oXB6gTEt+9XnA4BcmkBUDlzCbPUYBUM= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: TL; DR: sashiko found no blocker of this patch. Forwarding full sashiko review in a reply format with my inline comments below, for sharing details of my view and doing followup discussions via mails if needed. > # review url: https://sashiko.dev/#/patchset/20260411213638.77768-1-sj@kernel.org > # start of sashiko.dev inline review > commit a125056db470cab021e84ad481a0f51ddfc426c2 > Author: SeongJae Park > > mm/damon/core: disallow non-power of two min_region_sz on damon_start() > > This commit fixes an issue that allows unaligned DAMON region address ranges. > It adds a check for power-of-two min_region_sz directly in damon_start() > to catch invalid configurations from the sysfs interface. > > Link: https://lore.kernel.org/20260403155530.64647-1-sj@kernel.org > > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > index 3703f62a876b3..c107d74c77e74 100644 > > --- a/mm/damon/core.c > > +++ b/mm/damon/core.c > > @@ -1368,6 +1368,11 @@ int damon_start(struct damon_ctx **ctxs, int nr_ctxs, bool exclusive) > > int i; > > int err = 0; > > > > + for (i = 0; i < nr_ctxs; i++) { > > + if (!is_power_of_2(ctxs[i]->min_region_sz)) > > + return -EINVAL; > > + } > > + > > This isn't a regression introduced by this commit, but modifying > damon_start() brings up a question about partial failure handling when > starting multiple contexts. > > If __damon_start() succeeds for the first context but fails for a subsequent > one (for example if kthread_run() fails), the initialization loop breaks and > returns an error: > > for (i = 0; i < nr_ctxs; i++) { > err = __damon_start(ctxs[i]); > if (err) > break; > nr_running_ctxs++; > } > > Does this leave the previously successful kdamond threads running without > stopping them? > > Because nr_running_ctxs is incremented for the successful starts and > running_exclusive_ctxs is set to true, it appears the internal state > would prevent starting new contexts. > > Would this result in all future calls to damon_start() returning -EBUSY? Yes, this is not ideal. But as Sashiko also says it is no blocker of this patch. I will revisit this later. > > > # end of sashiko.dev inline review > # review url: https://sashiko.dev/#/patchset/20260411213638.77768-1-sj@kernel.org Thanks, SJ # hkml [1] generated a draft of this mail. You can regenerate # this using below command: # # hkml patch sashiko_dev --for_forwarding \ # 20260411213638.77768-1-sj@kernel.org # # [1] https://github.com/sjp38/hackermail