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=-13.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 BA320C5519F for ; Thu, 19 Nov 2020 00:14:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 63F0D246BB for ; Thu, 19 Nov 2020 00:14:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="QnL0x2Bf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726890AbgKSAOF (ORCPT ); Wed, 18 Nov 2020 19:14:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45168 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726243AbgKSAOF (ORCPT ); Wed, 18 Nov 2020 19:14:05 -0500 Received: from mail-wr1-x443.google.com (mail-wr1-x443.google.com [IPv6:2a00:1450:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 36E05C0613D4 for ; Wed, 18 Nov 2020 16:14:05 -0800 (PST) Received: by mail-wr1-x443.google.com with SMTP id c17so4469638wrc.11 for ; Wed, 18 Nov 2020 16:14:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=YPo2K8Ysp+BJYwVZ1P630QPIH7ch4pOcABLbBuoWFk8=; b=QnL0x2BfzgzPw3kCIk//9wYnmzoowBIagAcw23vCTE3RcyYSIlfgGV6Vx9kPlwdgS6 oeTLh6q3DeAI2yKlhjKExmKZXQTuWlVeYh4GpOjMfavJb4OesMOsL+G6HeQKijrsiF6K MQO+r9eBO7Rcwz1JVWxGiCwSjO/ZzetUi1AsequqSomDss/h1Mlr2lx5XUE8a1JLuR4T XAGWgTQIu0CjT1vFwJpEX2ETdrXtNKErdQdR/bLAvHgI79TxMuoyu60WQgcsDWjrLB1W UeKgIk77FW9UQns++O/pM3kp0Pr+X7o8KcUCDzRgmXsSXRJNQCV1Z9TjmmWkHcWwlvhO KkiA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=YPo2K8Ysp+BJYwVZ1P630QPIH7ch4pOcABLbBuoWFk8=; b=OcN3yW5Ux8jtXYGjKYYFsvBzIhuXHeuxMgXTTUpc7qgdZP9UhbX1OPRvq973I7EYEW S4yJ9DKCu63XLiGOkXtNcF01/9ViaZIyllzNqxBkdc/PcdNvuXVKlGKJ2N3dkx7Mmu72 xmRpp8dtSRMPos0NLXOkdGaH+ZC/sYxPj+ANKgGom6ioxcrhw24y6ji95/urp4+Io0yc ng7WKSa+mQXxYcp3V0O8wGpXEeAps0xv1wRiT+6CcTLsd7ob+jO0RpYtqlOXtgPzmX1u MH52XIt7uXv1Wn7kSgV7xQ7J0xa5rxi2KU+mdhhH+hagjlMrdKGa03ZMj9d7H+nG2w2X Uh1A== X-Gm-Message-State: AOAM532FTm7T2VJ7DhydA5LBlHMzoUCEyLjMbS4WA4ADuDCTdkRmII47 2G7nmgmIBrOWf8NZwWV04MCv/VObSeqbkhY2bZP+6Q== X-Google-Smtp-Source: ABdhPJwJOlh+PBDdhrK/i5u3QvrR6SX/KiEc/iISFTPiMtN06cL2iBTLuYMrsKeRZ46NdRAfk4/Y5fsyaYPo9N3zFoo= X-Received: by 2002:adf:cf0b:: with SMTP id o11mr7081447wrj.162.1605744843682; Wed, 18 Nov 2020 16:14:03 -0800 (PST) MIME-Version: 1.0 References: <20201113173448.1863419-1-surenb@google.com> <20201113155539.64e0af5b60ad3145b018ab0d@linux-foundation.org> <20201113170032.7aa56ea273c900f97e6ccbdc@linux-foundation.org> <20201113171810.bebf66608b145cced85bf54c@linux-foundation.org> <20201113181632.6d98489465430a987c96568d@linux-foundation.org> <20201118154334.GT12284@dhcp22.suse.cz> <20201118193233.GV12284@dhcp22.suse.cz> In-Reply-To: From: Suren Baghdasaryan Date: Wed, 18 Nov 2020 16:13:52 -0800 Message-ID: Subject: Re: [PATCH 1/1] RFC: add pidfd_send_signal flag to reclaim mm while killing a process To: Michal Hocko Cc: Andrew Morton , David Rientjes , Matthew Wilcox , Johannes Weiner , Roman Gushchin , Rik van Riel , Christian Brauner , Oleg Nesterov , Tim Murray , linux-api@vger.kernel.org, linux-mm , LKML , kernel-team , Minchan Kim Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Wed, Nov 18, 2020 at 11:55 AM Suren Baghdasaryan wrote: > > On Wed, Nov 18, 2020 at 11:51 AM Suren Baghdasaryan wrote: > > > > On Wed, Nov 18, 2020 at 11:32 AM Michal Hocko wrote: > > > > > > On Wed 18-11-20 11:22:21, Suren Baghdasaryan wrote: > > > > On Wed, Nov 18, 2020 at 11:10 AM Michal Hocko wrote: > > > > > > > > > > On Fri 13-11-20 18:16:32, Andrew Morton wrote: > > > > > [...] > > > > > > It's all sounding a bit painful (but not *too* painful). But to > > > > > > reiterate, I do think that adding the ability for a process to shoot > > > > > > down a large amount of another process's memory is a lot more generally > > > > > > useful than tying it to SIGKILL, agree? I was looking into how to work around the limitation of MAX_RW_COUNT and the conceptual issue there is the "struct iovec" which has its iov_len as size_t that lacks capacity for expressing ranges like "entire process memory". I would like to check your reaction to the following idea which can be implemented without painful surgeries to the import_iovec and its friends. process_madvise(pidfd, iovec = [ { range_start_addr, 0 }, { range_end_addr, 0 } ], vlen = 2, behavior=MADV_xxx, flags = PMADV_FLAG_RANGE) So, to represent a range we pass a new PMADV_FLAG_RANGE flag and construct a 2-element vector to express range start and range end using iovec.iov_base members. iov_len member of the iovec elements is ignored in this mode. I know it sounds hacky but I think it's the simplest way if we want the ability to express an arbitrarily large range. Another option is to do what Andrew described as "madvise((void *)0, (void *)-1, MADV_PAGEOUT)" which means this mode works only with the entire mm of the process. WDYT? > > > > > > > > > > I am not sure TBH. Is there any reasonable usecase where uncoordinated > > > > > memory tear down is OK and a target process which is able to see the > > > > > unmapped memory? > > > > > > > > I think uncoordinated memory tear down is a special case which makes > > > > sense only when the target process is being killed (and we can enforce > > > > that by allowing MADV_DONTNEED to be used only if the target process > > > > has pending SIGKILL). > > > > > > That would be safe but then I am wondering whether it makes sense to > > > implement as a madvise call. It is quite strange to expect somebody call > > > a syscall on a killed process. But this is more a detail. I am not a > > > great fan of a more generic MADV_DONTNEED on a remote process. This is > > > just too dangerous IMHO. > > > > Agree 100% > > I assumed here that by "a more generic MADV_DONTNEED on a remote > process" you meant "process_madvise(MADV_DONTNEED) applied to a > process that is not being killed". Re-reading your comment I realized > that you might have meant "process_madvice() with generic support to > large memory areas". I hope I understood you correctly. > > > > > > > > > > However, the ability to apply other flavors of > > > > process_madvise() to large memory areas spanning multiple VMAs can be > > > > useful in more cases. > > > > > > Yes I do agree with that. The error reporting would be more tricky but > > > I am not really sure that the exact reporting is really necessary for > > > advice like interface. > > > > Andrew's suggestion for this special mode to change return semantics > > to the usual "0 or error code" seems to me like the most reasonable > > way to deal with the return value limitation. > > > > > > > > > For example in Android we will use > > > > process_madvise(MADV_PAGEOUT) to "shrink" an inactive background > > > > process. > > > > > > That makes sense to me. > > > -- > > > Michal Hocko > > > SUSE Labs