From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 337542A1B2 for ; Thu, 25 Dec 2025 01:07:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766624850; cv=none; b=Ntc2AjIK1xe5mBd/x6R/Ex9YKD4YqxnGzTXMgnefo9nV5f5o2Rg8Qdyc3hhA6vMFfCUJPz5AKDAm+m/PLu/0w28jriHWCRbmnEDKt4LCpXkzNDdce6vO6NvQJnEW08iX7aepE+RJHv8EEdLO7xh1qHWnY1PoaOtrrP8NT/S2qBg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766624850; c=relaxed/simple; bh=AI9rBkTfUwqknwjaDpIIAVHasx1YLalXCFloURsFIag=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=G6eShIaPz/xYqwvGpy8+FAT3XrmlWrRNOMcM90FI+wKZqqnZ8lXPf4Dkjg5wnW7eO6/cP9oIfsmA6nQIg/7S5pionQtWlj4ItQI+HnbNGxr+Qqher9u6/xXJRmTHMLQMPhdyWw6DO7hLCPRuVGjiqbbYXmIuvLTuUFj6ZaCYhoM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A7n7o4qI; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="A7n7o4qI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8A0F4C4CEF7; Thu, 25 Dec 2025 01:07:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766624849; bh=AI9rBkTfUwqknwjaDpIIAVHasx1YLalXCFloURsFIag=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=A7n7o4qIqBAS50cMbyAzX2vGXpbmTQTH8YAawbEinmTeKB/ThmYU5wKvETkRKsTyb eeAjlx5DoF4vlDOh8Bw3QuN5nXIRPbE+zb3DAPAoyEQ6zBaFM11hV2n4o9LEUqgfby 26dq65ASK+wE4v2ajYjM42VZlN08X0scfGCWeCJRktJhHT9FwZFo3wFpKOcA+5mEGX MDp8ja0uGqwKxqs3fPuOcCf3URFBfYogLMwSaY5FndsSlrodZ7CRQTsD+Hjo362dbn 9qFQze58t/Ur/qcTj36gnP++vHy9pJNozh2aOIJ4SZxVYIve3Q5bSug1jTc10UaNDe wwbsqX8svz5NQ== From: SeongJae Park To: JaeJoon Jung Cc: SeongJae Park , damon@lists.linux.dev, linux-mm@kvack.org, rgbi3307@nate.com Subject: Re: [PATCH] mm/damon/core: modified control->repeat loop at the kdamond_call() Date: Wed, 24 Dec 2025 17:07:21 -0800 Message-ID: <20251225010722.14746-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251224124355.31667-1-rgbi3307@gmail.com> References: Precedence: bulk X-Mailing-List: damon@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Wed, 24 Dec 2025 21:43:54 +0900 JaeJoon Jung wrote: > The kdamond_call() function is executed repeatedly in the kdamond_fn() > kernel thread. The kdamond_call() function is implemented as a while loop. > Therefore, it is important to improve the list processing logic here to > ensure faster execution of control->fn(). That depends on how critical the performance is, and how much complexity the optimization introduces. I have no idea about if the performance of kdamond_call() is really important. If you have a realistic use case that shows it, sharing it would be nice. > For ease of explanation, > the data structure names will be abbreviated as follows: > > damon_call_control.list: C.list > ctx->call_controls: CTX.head > repeat_controls: R.head > > the execution flow of the while loop of the kdamond_call() function, > > Before modification: > Old while loop: > > CTX.head <-----> C.list <-----> C.list <----> C.list > ^ | | > | if (C.repeat) if (!C.repeat) > restore: only one | | > list_add_tail() list_del() list_del() > | | | > + | complete() > R.head <------ list_add() > > To process C.repeat above, we use an additional list, repeat_controls. Your above abbreviation didn't explain what C.repeat is. Maybe you mean 'damon_call_control.repeat'? > The process of adding C.list to repeat_controls and then restoring it back > to CTX.head is complex and inefficient. I agree. > Furthermore, there's the problem > of restoring only a single C.list to CTX.head. I had to take some time on understanding what this mean. And it seems you are working on an old version of the tree, and therefore saying about an issue that already fixed by commit 592e5c5f8ec6 ("mm/damon/core: fix memory leak of repeat mode damon_call_control objects"). Please use mm-new as a baseline of DAMON patches, unless there are special reasons. If there are special reasons, please explicitly specify. > > Below, repeat_controls is removed and the existing CTX.head is modified to > loop once(1st rotation). This simplifies list processing and creates a > more efficient structure. > > Modified while loop: > Not used repeat_controls: > > CTX.head <-----> C.list <-----> C.list <----> C.list <-------+ > | | | > if (C.repeat) if (!C.repeat) | > | | | > list_del() list_del() | > | | | > | complete() | > | | > first --------> list_add_tail() -----------+ > > if (C.list == first) break; > > Signed-off-by: JaeJoon Jung > --- > mm/damon/core.c | 37 +++++++++++++++++++------------------ > 1 file changed, 19 insertions(+), 18 deletions(-) > > diff --git a/mm/damon/core.c b/mm/damon/core.c > index 824aa8f22db3..babad37719b6 100644 > --- a/mm/damon/core.c > +++ b/mm/damon/core.c > @@ -2554,42 +2554,43 @@ static void kdamond_usleep(unsigned long usecs) > */ > static void kdamond_call(struct damon_ctx *ctx, bool cancel) > { > - struct damon_call_control *control; > - LIST_HEAD(repeat_controls); > - int ret = 0; > + struct damon_call_control *control, *first = NULL; > + unsigned int idx = 0; > > while (true) { > mutex_lock(&ctx->call_controls_lock); > control = list_first_entry_or_null(&ctx->call_controls, > struct damon_call_control, list); > mutex_unlock(&ctx->call_controls_lock); > - if (!control) > + > + /* check control empty or 1st rotation */ > + if (!control || control == first) > break; > - if (cancel) { > + > + if (++idx == 1) > + first = control; > + > + if (cancel) > control->canceled = true; > - } else { > - ret = control->fn(control->data); > - control->return_code = ret; > - } > + else > + control->return_code = control->fn(control->data); > + > mutex_lock(&ctx->call_controls_lock); > list_del(&control->list); > mutex_unlock(&ctx->call_controls_lock); > + > if (!control->repeat) { > + /* run control->fn() one time */ > complete(&control->completion); > } else if (control->canceled && control->dealloc_on_cancel) { > kfree(control); > - continue; > } else { > - list_add(&control->list, &repeat_controls); > + /* to repeat next time */ > + mutex_lock(&ctx->call_controls_lock); > + list_add_tail(&control->list, &ctx->call_controls); > + mutex_unlock(&ctx->call_controls_lock); > } > } Let's suppose there are two damon_call_control objects on the ctx->call_controls. The first one has ->repeat unset, while the second one has. Then, it seems the 'break' condition will never met and therefore this loop will never finished. Am I missing something? > - control = list_first_entry_or_null(&repeat_controls, > - struct damon_call_control, list); > - if (!control || cancel) > - return; > - mutex_lock(&ctx->call_controls_lock); > - list_add_tail(&control->list, &ctx->call_controls); > - mutex_unlock(&ctx->call_controls_lock); As I mentioned above, apparently you are using an old version of the tree that not having commit 592e5c5f8ec6 ("mm/damon/core: fix memory leak of repeat mode damon_call_control objects") that modified this part. Please use mm-new as a baseline, or specify reasons why you cannot do so. > } > > /* Returns negative error code if it's not activated but should return */ > -- > 2.43.0 Thanks, SJ