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Mon, 04 Nov 2019 21:15:06 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.27/8.16.0.27) with SMTP id xA4L3ioJ148578; Mon, 4 Nov 2019 21:15:06 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3030.oracle.com with ESMTP id 2w1k8vh5tf-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 04 Nov 2019 21:15:05 +0000 Received: from abhmp0016.oracle.com (abhmp0016.oracle.com [141.146.116.22]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id xA4LF3CE029403; Mon, 4 Nov 2019 21:15:03 GMT Received: from [192.168.1.206] (/71.63.128.209) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 04 Nov 2019 13:15:03 -0800 Subject: Re: [PATCH v8 5/9] hugetlb: disable region_add file_region coalescing To: Mina Almasry Cc: shuah , open list , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, cgroups@vger.kernel.org, Aneesh Kumar References: <20191030013701.39647-1-almasrymina@google.com> <20191030013701.39647-5-almasrymina@google.com> <1c060bde-8d44-146c-6d67-a7b145aa1b59@oracle.com> From: Mike Kravetz Message-ID: Date: Mon, 4 Nov 2019 13:15:02 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9431 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1911040203 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9431 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1911040203 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/4/19 1:04 PM, Mina Almasry wrote: > On Fri, Nov 1, 2019 at 4:23 PM Mike Kravetz wrote: >> >> On 10/29/19 6:36 PM, Mina Almasry wrote: >>> static long add_reservation_in_range(struct resv_map *resv, long f, long t, >>> - bool count_only) >>> + long *regions_needed, bool count_only) >>> { >>> - long chg = 0; >>> + long add = 0; >>> struct list_head *head = &resv->regions; >>> + long last_accounted_offset = f; >>> struct file_region *rg = NULL, *trg = NULL, *nrg = NULL; >>> >>> - /* Locate the region we are before or in. */ >>> - list_for_each_entry (rg, head, link) >>> - if (f <= rg->to) >>> - break; >>> + if (regions_needed) >>> + *regions_needed = 0; >>> >>> - /* Round our left edge to the current segment if it encloses us. */ >>> - if (f > rg->from) >>> - f = rg->from; >>> - >>> - chg = t - f; >>> + /* In this loop, we essentially handle an entry for the range >>> + * [last_accounted_offset, rg->from), at every iteration, with some >>> + * bounds checking. >>> + */ >>> + list_for_each_entry_safe(rg, trg, head, link) { >>> + /* Skip irrelevant regions that start before our range. */ >>> + if (rg->from < f) { >>> + /* If this region ends after the last accounted offset, >>> + * then we need to update last_accounted_offset. >>> + */ >>> + if (rg->to > last_accounted_offset) >>> + last_accounted_offset = rg->to; >>> + continue; >>> + } >>> >>> - /* Check for and consume any regions we now overlap with. */ >>> - nrg = rg; >>> - list_for_each_entry_safe (rg, trg, rg->link.prev, link) { >>> - if (&rg->link == head) >>> - break; >>> + /* When we find a region that starts beyond our range, we've >>> + * finished. >>> + */ >>> if (rg->from > t) >>> break; >>> >>> - /* We overlap with this area, if it extends further than >>> - * us then we must extend ourselves. Account for its >>> - * existing reservation. >>> + /* Add an entry for last_accounted_offset -> rg->from, and >>> + * update last_accounted_offset. >>> */ >>> - if (rg->to > t) { >>> - chg += rg->to - t; >>> - t = rg->to; >>> + if (rg->from > last_accounted_offset) { >>> + add += rg->from - last_accounted_offset; >>> + if (!count_only) { >>> + nrg = get_file_region_entry_from_cache( >>> + resv, last_accounted_offset, rg->from); >>> + list_add(&nrg->link, rg->link.prev); >>> + } else if (regions_needed) >>> + *regions_needed += 1; >>> } >>> - chg -= rg->to - rg->from; >>> >>> - if (!count_only && rg != nrg) { >>> - list_del(&rg->link); >>> - kfree(rg); >>> - } >>> + last_accounted_offset = rg->to; >> >> That last assignment is unneeded. Correct? >> > > Not to make you nervous, but this assignment is needed. > > The basic idea is that there are 2 loop invariants here: > 1. Everything before last_accounted_offset is filled in with file_regions. > 2. rg points to the first region past last_account_offset. > > Each loop iteration compares rg->from to last_accounted_offset, and if > there is a gap, it creates a new region to fill this gap. Then this > assignment restores loop invariant #2 by assigning > last_accounted_offset to rg->to, since now everything before rg->to is > filled in with file_regions. > My apologies! >>> } >>> >>> - if (!count_only) { >>> - nrg->from = f; >>> - nrg->to = t; >>> + /* Handle the case where our range extends beyond >>> + * last_accounted_offset. >>> + */ >>> + if (last_accounted_offset < t) { >>> + add += t - last_accounted_offset; >>> + if (!count_only) { >>> + nrg = get_file_region_entry_from_cache( >>> + resv, last_accounted_offset, t); >>> + list_add(&nrg->link, rg->link.prev); >>> + } else if (regions_needed) >>> + *regions_needed += 1; >>> + last_accounted_offset = t; The question about an unnecessary assignment was supposed to be directed at the above line. -- Mike Kravetz >>> } >>> >>> - return chg; >>> + return add; >>> }