From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 891AC385734D for ; Tue, 11 Oct 2022 11:06:12 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 891AC385734D Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1665486372; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=fecOUojzntCs6+YwNzWxP4JJxAQBG7DnF18zz1fEiiI=; b=BptAud02NjLSkYWRgDM2HF+Ia3d4zKpONalS4o4YLWk/xJ9XnSJq3+S9em9F1Ej1mP8g2b NheicZO79TsZjSXqIH5rh7hIHKCnmM+ZR8UpZv7bo91u7tNPd6Zn9rvB68jVHfZZMO5+5D aonF7fdcLZUCsHamIVqOIbsLnxUpUEY= Received: from mail-qk1-f200.google.com (mail-qk1-f200.google.com [209.85.222.200]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-164-Uj6Qq9DCNKGIJmo6R00kSQ-1; Tue, 11 Oct 2022 07:06:10 -0400 X-MC-Unique: Uj6Qq9DCNKGIJmo6R00kSQ-1 Received: by mail-qk1-f200.google.com with SMTP id bs30-20020a05620a471e00b006ed2a84071bso3630046qkb.0 for ; Tue, 11 Oct 2022 04:06:10 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=fecOUojzntCs6+YwNzWxP4JJxAQBG7DnF18zz1fEiiI=; b=nj1pzZ17UUG1fgJqurLHtI/iVC2Blzcmly4+Q9ysD/hqbyHMnBGEFGL6AJT3VApAV+ c7hJ0i0SykbuwU6tRtTSfiDXFutJji2nl8ov6UG+lKHb+Xf5/I9P6pEqgRIDQsQYCxmQ 2hMQHQF1gJZ/oZyMPVhKzw7fdROpONLy4b/9XuJmTkOiK+pvl4Yx/kjXhcksedaIBpyH TAVLJPBjseUfjpMvKZOL2O1WKG6jCHnZB0x/dKFO6mQhohYijXc6EsULtpS9c6F9JzIS j30wV5jCjhaVCqJsRSo8K+udMxmoQpXFxT9e5dpEd4IjRW0otsahO3m1fqtvCY1XMU9r 9rIw== X-Gm-Message-State: ACrzQf3vXNYYcHNVSdke3uEmqkeRMC8boNSxbtFEQXhHHiAitVdWhKsg txaP6kAU5Ckwl3Q+Pt5EZlZUD5O/2ny0AiYw9QEXBT9mLP1nZBzUkDtqCmHogx2IzB7X4YqizMh goEWU8JLhMOBOP9CU5gCelP+vGyfwHgs= X-Received: by 2002:ad4:5deb:0:b0:4b1:d1cc:7cef with SMTP id jn11-20020ad45deb000000b004b1d1cc7cefmr18006291qvb.124.1665486370017; Tue, 11 Oct 2022 04:06:10 -0700 (PDT) X-Google-Smtp-Source: AMsMyM6ozdgLTVB3mfj0yx47k5hQImU1++cSkOf11+9mJYriz60lUAX/SkIZydhNdFOtKmxqfxPKBL6PvckrdRwrJcg= X-Received: by 2002:ad4:5deb:0:b0:4b1:d1cc:7cef with SMTP id jn11-20020ad45deb000000b004b1d1cc7cefmr18006276qvb.124.1665486369752; Tue, 11 Oct 2022 04:06:09 -0700 (PDT) MIME-Version: 1.0 References: <20221007155452.1299670-1-jwakely@redhat.com> In-Reply-To: From: Jonathan Wakely Date: Tue, 11 Oct 2022 12:05:59 +0100 Message-ID: Subject: Re: [PATCH] libstdc++: Allow emergency EH alloc pool size to be tuned [PR68606] To: Richard Biener Cc: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-6.7 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Tue, 11 Oct 2022 at 07:41, Richard Biener wrote: > > On Mon, Oct 10, 2022 at 5:10 PM Jonathan Wakely wrote: > > > > On Mon, 10 Oct 2022 at 12:17, Jonathan Wakely wrote: > > > > > > On Mon, 10 Oct 2022 at 07:18, Richard Biener wrote: > > > > > > > > On Fri, Oct 7, 2022 at 5:55 PM Jonathan Wakely via Gcc-patches > > > > wrote: > > > > > > > > > > This needs a little more documentation (see the TODO in the manual), > > > > > rather than just the comments in the source. This isn't final, but I > > > > > think it's the direction I want to take. > > > > > > > > > > -- >8 -- > > > > > > > > > > Implement a long-standing request to support tuning the size of the > > > > > emergency buffer for allocating exceptions after malloc fails, or to > > > > > disable that buffer entirely. > > > > > > > > > > It's now possible to disable the dynamic allocation of the buffer and > > > > > use a fixed-size static buffer, via --enable-libstdcxx-static-eh-pool. > > > > > This is a built-time choice that is baked into libstdc++ and so affects > > > > > all code linked against that build of libstdc++. > > > > > > > > > > The size of the pool can be set by --with-libstdcxx-eh-pool-obj-count=N > > > > > which is measured in units of sizeof(void*) not bytes. A given exception > > > > > type such as std::system_error depends on the target, so giving a size > > > > > in bytes wouldn't be portable across 16/32/64-bit targets. > > > > > > > > > > When libstdc++ is configured to use a dynamic buffer, the size of that > > > > > buffer can now be tuned at runtime by setting the GLIBCXX_TUNABLES > > > > > environment variable (c.f. PR libstdc++/88264). The number of exceptions > > > > > to reserve space for is controlled by the "glibcxx.eh_pool.obj_count" > > > > > and "glibcxx.eh_pool.obj_size" tunables. The pool will be sized to be > > > > > able to allocate obj_count exceptions of size obj_size*sizeof(void*) and > > > > > obj_count "dependent" exceptions rethrown by std::rethrow_exception. > > > > > > > > > > With the ability to tune the buffer size, we can reduce the default pool > > > > > size. Most users never need to throw 1kB exceptions in parallel from > > > > > hundreds of threads after malloc is OOM. > > > > > > > > But does it hurt? Back in time when I reworked the allocator to be less > > > > wasteful the whole point was to allow more exceptions to be in-flight > > > > during OOM shutdown of a process with many threads. > > > > > > It certainly hurts for small systems, but maybe we can keep the large > > > allocation for 64-bit targets (currently 73kB) and only reduce it for > > > 32-bit (19kB) and 16-bit (3kB IIRC) targets. > > > > Maybe this incremental diff would be an improvement: > > > > @@ -90,7 +90,7 @@ using namespace __cxxabiv1; > > // Assume that the number of concurrent exception objects scales with the > > // processor word size, i.e., 16-bit systems are not likely to have hundreds > > // of threads all simultaneously throwing on OOM conditions. > > -# define EMERGENCY_OBJ_COUNT (8 * __SIZEOF_POINTER__) > > +# define EMERGENCY_OBJ_COUNT (4 * __SIZEOF_POINTER__ * __SIZEOF_POINTER__) > > # define MAX_OBJ_COUNT (16 << __SIZEOF_POINTER__) > > #else > > # define EMERGENCY_OBJ_COUNT 4 > > > > This makes it quadratic in the word size, so on 64-bit targets we'd > > have space for 256 "reasonable size" exceptions (and twice as many > > single word exceptions like std::bad_alloc), but only 64 on 32-bit > > targets, and only 16 on 16-bit ones. > > So can we then commonize some of the #defines by using sizeof(void *) > (taking pointer size as word size?) What did you have in mind? Do you mean use sizeof(void*) instead of the SIZEOF macro? MAX_OBJ_COUNT uses the SIZEOF macro so it can be used in a preprocessor condition: #ifdef _GLIBCXX_EH_POOL_NOBJS # if _GLIBCXX_EH_POOL_NOBJS > MAX_OBJ_COUNT