From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f70.google.com (mail-it0-f70.google.com [209.85.214.70]) by kanga.kvack.org (Postfix) with ESMTP id 33D88280281 for ; Wed, 17 Jan 2018 04:49:53 -0500 (EST) Received: by mail-it0-f70.google.com with SMTP id z142so6447359itc.6 for ; Wed, 17 Jan 2018 01:49:53 -0800 (PST) Received: from huawei.com (szxga05-in.huawei.com. [45.249.212.191]) by mx.google.com with ESMTPS id u185si1948910ioe.331.2018.01.17.01.49.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Jan 2018 01:49:52 -0800 (PST) Message-ID: <5A5F1C09.9040000@huawei.com> Date: Wed, 17 Jan 2018 17:48:57 +0800 From: Xishi Qiu MIME-Version: 1.0 Subject: Re: [RFC] mm: why vfree() do not free page table memory? References: <5A4603AB.8060809@huawei.com> <0ffd113e-84da-bd49-2b63-3d27d2702580@suse.cz> In-Reply-To: <0ffd113e-84da-bd49-2b63-3d27d2702580@suse.cz> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka Cc: Michal Hocko , Mel Gorman , LKML , Linux MM , "Wujiangtao (A)" On 2018/1/17 17:16, Vlastimil Babka wrote: > On 12/29/2017 09:58 AM, Xishi Qiu wrote: >> When calling vfree(), it calls unmap_vmap_area() to clear page table, >> but do not free the memory of page table, why? just for performance? > > I guess it's expected that the free virtual range and associated page > tables it might be reused later. > Hi Vlastimili 1/4 ? If use vmalloc/vfree different size, then there will be some hols during VMALLOC_START to VMALLOC_END, and this holes takes page table memory, right? >> If a driver use vmalloc() and vfree() frequently, we will lost much >> page table memory, maybe oom later. > > If it's reused, then not really. > > Did you notice an actual issue, or is this just theoretical concern. > Yes, we have this problem on our production line. I find the page table memory takes 200-300M. Thanks, Xishi Qiu >> Thanks, >> Xishi Qiu >> > > > . > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org