From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A657BC10F27 for ; Tue, 10 Mar 2020 11:51:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 509672464B for ; Tue, 10 Mar 2020 11:51:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amazon.com header.i=@amazon.com header.b="EfJDB/YP" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 509672464B Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=amazon.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D3F636B000A; Tue, 10 Mar 2020 07:51:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CEF006B000C; Tue, 10 Mar 2020 07:51:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BDF3E6B000D; Tue, 10 Mar 2020 07:51:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0026.hostedemail.com [216.40.44.26]) by kanga.kvack.org (Postfix) with ESMTP id A75CB6B000A for ; Tue, 10 Mar 2020 07:51:43 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 9CC2F181AEF00 for ; Tue, 10 Mar 2020 11:51:43 +0000 (UTC) X-FDA: 76579288086.15.hate59_efd451928c09 X-HE-Tag: hate59_efd451928c09 X-Filterd-Recvd-Size: 11229 Received: from smtp-fw-9101.amazon.com (smtp-fw-9101.amazon.com [207.171.184.25]) by imf34.hostedemail.com (Postfix) with ESMTP for ; Tue, 10 Mar 2020 11:51:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1583841103; x=1615377103; h=from:to:cc:subject:date:message-id:in-reply-to: mime-version; bh=QvNs1X7gKJs6PKCVvsd9lF/RMXQloNFCJCkTdzItMqI=; b=EfJDB/YPxjj42qAUqJdOHJq6zY6itIGYyMnsqwpmfPNuFvw+6781BxEB tsIn7wksCRyK5JDLZJhtTVxn5R6/qzNDaNnUvoMcRFpPO8jx0NwivHheA ECSVEI4IqhBRsTE20QuXZRm9PTESIDggNlCFuas/bF5ltNsGkRGQRcZuT Q=; IronPort-SDR: EJZjgMY1z4JO4meBWbMtPFhhohLkgKyE4FrzhbW7JJeLnTfjpaufc8GwDNRQhYioSC1c9LtcTI hhki5B93VJBw== X-IronPort-AV: E=Sophos;i="5.70,536,1574121600"; d="scan'208";a="21950597" Received: from sea32-co-svc-lb4-vlan3.sea.corp.amazon.com (HELO email-inbound-relay-1a-af6a10df.us-east-1.amazon.com) ([10.47.23.38]) by smtp-border-fw-out-9101.sea19.amazon.com with ESMTP; 10 Mar 2020 11:51:38 +0000 Received: from EX13MTAUEA002.ant.amazon.com (iad55-ws-svc-p15-lb9-vlan3.iad.amazon.com [10.40.159.166]) by email-inbound-relay-1a-af6a10df.us-east-1.amazon.com (Postfix) with ESMTPS id 473CCA06F9; Tue, 10 Mar 2020 11:51:27 +0000 (UTC) Received: from EX13D31EUA001.ant.amazon.com (10.43.165.15) by EX13MTAUEA002.ant.amazon.com (10.43.61.77) with Microsoft SMTP Server (TLS) id 15.0.1236.3; Tue, 10 Mar 2020 11:51:27 +0000 Received: from u886c93fd17d25d.ant.amazon.com (10.43.161.152) by EX13D31EUA001.ant.amazon.com (10.43.165.15) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 10 Mar 2020 11:51:15 +0000 From: SeongJae Park To: Jonathan Cameron CC: SeongJae Park , , "SeongJae Park" , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: Re: [PATCH v6 01/14] mm: Introduce Data Access MONitor (DAMON) Date: Tue, 10 Mar 2020 12:50:59 +0100 Message-ID: <20200310115059.22831-1-sjpark@amazon.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200310085405.000061af@Huawei.com> (raw) MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.43.161.152] X-ClientProxiedBy: EX13D04UWB004.ant.amazon.com (10.43.161.103) To EX13D31EUA001.ant.amazon.com (10.43.165.15) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 10 Mar 2020 08:54:05 +0000 Jonathan Cameron wrote: > Apologies if anyone gets these twice. I had an email server throttling > issue yesterday. > > On Mon, 24 Feb 2020 13:30:34 +0100 > SeongJae Park wrote: > > > From: SeongJae Park > > > > This commit introduces a kernel module named DAMON. Note that this > > commit is implementing only the stub for the module load/unload, basic > > data structures, and simple manipulation functions of the structures to > > keep the size of commit small. The core mechanisms of DAMON will be > > implemented one by one by following commits. > > Interesting piece of work. I'm reviewing this partly as an exercise in > understanding it, but I'll point out minor stuff on the basis I might > as well whilst I'm here. ;) Note I review bottom up so some comments > won't make much sense read from the top. Thanks for review, Jonathan :) I added reply in line below, but agree to your whole suggestion. Will apply those in next spin. > > > > > Brief Introduction > > ================== > > I'd keep this level of intro for the cover letter / docs. It's not > particularly useful in commit message it git. Agreed. > > > [...] > > > > +config DAMON > > + tristate "Data Access Monitor" > > + depends on MMU > > + default n > > No need to specify a default of n. Got it. > > > + help > > + Provides data access monitoring. > > + > > + DAMON is a kernel module that allows users to monitor the actual > > + memory access pattern of specific user-space processes. It aims to > > + be 1) accurate enough to be useful for performance-centric domains, > > + and 2) sufficiently light-weight so that it can be applied online. > > + > > endmenu [...] > > +/* > > + * Construct a damon_region struct > > + * > > + * Returns the pointer to the new struct if success, or NULL otherwise > > + */ > > +static struct damon_region *damon_new_region(struct damon_ctx *ctx, > > + unsigned long vm_start, unsigned long vm_end) > > +{ > > + struct damon_region *ret; > > I'd give this a different variable name. Expectation in kernel is often > that ret is simply an magic handle to be passed on. Don't normally expect > to set elements of it. I'd go long hand and call it region. Nice point, will change the name to 'region'. > > > + > > + ret = kmalloc(sizeof(struct damon_region), GFP_KERNEL); > > sizeof(*ret) Thanks for catching it! Will apply to other similar cases. > > > + if (!ret) > > + return NULL; > > blank line. Good suggestion. > > > + ret->vm_start = vm_start; > > + ret->vm_end = vm_end; > > + ret->nr_accesses = 0; > > + ret->sampling_addr = damon_rand(ctx, vm_start, vm_end); > > + INIT_LIST_HEAD(&ret->list); > > + > > + return ret; > > +} > > + > > +/* > > + * Add a region between two other regions > Interestingly even the list.h comments for __list_add call this > function "insert". No idea why it isn't simply called that.. > > Perhaps damon_insert_region would be clearer and avoid need > for comment? I just wanted to make the name consistent with the 'list.h' file, but your suggestion sounds better. Will change so. > > > + */ > > +static inline void damon_add_region(struct damon_region *r, > > + struct damon_region *prev, struct damon_region *next) > > +{ > > + __list_add(&r->list, &prev->list, &next->list); > > +} > > + > > +/* > > + * Append a region to a task's list of regions > > I'd argue the naming is sufficient that the comment adds little. Yes, will delete it. > > > + */ > > +static void damon_add_region_tail(struct damon_region *r, struct damon_task *t) > > +{ > > + list_add_tail(&r->list, &t->regions_list); > > +} > > + > > +/* > > + * Delete a region from its list > > The list is an implementation detail. I'd not mention that in the comments. Nice suggestion. > > > + */ > > +static void damon_del_region(struct damon_region *r) > > +{ > > + list_del(&r->list); > > +} > > + > > +/* > > + * De-allocate a region > > Obvious comment - seem rot risk note below. Agreed. > > > + */ > > +static void damon_free_region(struct damon_region *r) > > +{ > > + kfree(r); > > +} > > + > > +static void damon_destroy_region(struct damon_region *r) > > +{ > > + damon_del_region(r); > > + damon_free_region(r); > > +} > > + > > +/* > > + * Construct a damon_task struct > > + * > > + * Returns the pointer to the new struct if success, or NULL otherwise > > + */ > > +static struct damon_task *damon_new_task(unsigned long pid) > > +{ > > + struct damon_task *t; > > + > > + t = kmalloc(sizeof(struct damon_task), GFP_KERNEL); > > sizeof(*t) is probably less error prone if this code is maintained > in the long run. Good point, will apply to other cases, either. > > > + if (!t) > > + return NULL; > > blank line. Will add it. > > > + t->pid = pid; > > + INIT_LIST_HEAD(&t->regions_list); > > + > > + return t; > > +} > > + > > +/* Returns n-th damon_region of the given task */ > > +struct damon_region *damon_nth_region_of(struct damon_task *t, unsigned int n) > > +{ > > + struct damon_region *r; > > + unsigned int i; > > + > > + i = 0; > unsigned int i = 0; Yes, it must be much better. > > > + damon_for_each_region(r, t) { > > + if (i++ == n) > > + return r; > > + } > > blank line helps readability a little. Yes, indeed. > > > + return NULL; > > +} > > + > > +static void damon_add_task_tail(struct damon_ctx *ctx, struct damon_task *t) > > I'm curious, do we care that it's on the tail? If not I'd look on that as an > implementation detail and just call this > > damon_add_task() I named it to be consistent with 'damon_add_region[_tail]()' functions, but as you suggested renaming 'damon_add_region()', it doesn't need to. Will change the name. > > > +{ > > + list_add_tail(&t->list, &ctx->tasks_list); > > +} > > + > > +static void damon_del_task(struct damon_task *t) > > +{ > > + list_del(&t->list); > > +} > > + > > +static void damon_free_task(struct damon_task *t) > > +{ > > + struct damon_region *r, *next; > > + > > + damon_for_each_region_safe(r, next, t) > > + damon_free_region(r); > > + kfree(t); > > +} > > + > > +static void damon_destroy_task(struct damon_task *t) > > +{ > > + damon_del_task(t); > > + damon_free_task(t); > > +} > > + > > +/* > > + * Returns number of monitoring target tasks > > As below, kind of obvious so just room for rot. Agreed. > > > + */ > > +static unsigned int nr_damon_tasks(struct damon_ctx *ctx) > > +{ > > + struct damon_task *t; > > + unsigned int ret = 0; > > + > > + damon_for_each_task(ctx, t) > > + ret++; > > + return ret; > > +} > > + > > +/* > > + * Returns the number of target regions for a given target task > > Always a trade off between useful comments and possibility of docs > rotting. I'd drop this comment certainly. > The function name is self explanatory. Agreed! > > > + */ > > +static unsigned int nr_damon_regions(struct damon_task *t) > > +{ > > + struct damon_region *r; > > + unsigned int ret = 0; > > + > > + damon_for_each_region(r, t) > > + ret++; > > Blank line here would help readability a tiny bit. > Same in other places where we have something followed by a nice > simple return statement. Yes, indeed. > > > + return ret; > > +} > > + > > +static int __init damon_init(void) > > +{ > > + pr_info("init\n"); > > Drop these. They are just noise. Right, it's just noise, will remove. Thank you again for kind review, Jonathan! Thanks, SeongJae Park > > > + > > + return 0; > > +} > > + > > +static void __exit damon_exit(void) > > +{ > > + pr_info("exit\n"); > > +} > > + > > +module_init(damon_init); > > +module_exit(damon_exit); > > + > > +MODULE_LICENSE("GPL"); > > +MODULE_AUTHOR("SeongJae Park "); > > +MODULE_DESCRIPTION("DAMON: Data Access MONitor"); >