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[185.107.14.3]) by smtp.gmail.com with ESMTPSA id k31sm2595939wms.31.2021.08.12.08.17.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Aug 2021 08:17:08 -0700 (PDT) From: Jesper Dangaard Brouer X-Google-Original-From: Jesper Dangaard Brouer Cc: brouer@redhat.com, alexander.duyck@gmail.com, linux@armlinux.org.uk, mw@semihalf.com, linuxarm@openeuler.org, yisen.zhuang@huawei.com, salil.mehta@huawei.com, thomas.petazzoni@bootlin.com, hawk@kernel.org, ilias.apalodimas@linaro.org, ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, akpm@linux-foundation.org, peterz@infradead.org, will@kernel.org, willy@infradead.org, vbabka@suse.cz, fenghua.yu@intel.com, guro@fb.com, peterx@redhat.com, feng.tang@intel.com, jgg@ziepe.ca, mcroce@microsoft.com, hughd@google.com, jonathan.lemon@gmail.com, alobakin@pm.me, willemb@google.com, wenxu@ucloud.cn, cong.wang@bytedance.com, haokexin@gmail.com, nogikh@google.com, elver@google.com, yhs@fb.com, kpsingh@kernel.org, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, chenhao288@hisilicon.com Subject: Re: [PATCH net-next v2 2/4] page_pool: add interface to manipulate frag count in page pool To: Yunsheng Lin , davem@davemloft.net, kuba@kernel.org References: <1628217982-53533-1-git-send-email-linyunsheng@huawei.com> <1628217982-53533-3-git-send-email-linyunsheng@huawei.com> Message-ID: Date: Thu, 12 Aug 2021 17:17:05 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <1628217982-53533-3-git-send-email-linyunsheng@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/08/2021 04.46, Yunsheng Lin wrote: > +static inline long page_pool_atomic_sub_frag_count_return(struct page *page, > + long nr) > +{ > + long ret; > + > + /* As suggested by Alexander, atomic_long_read() may cover up the > + * reference count errors, so avoid calling atomic_long_read() in > + * the cases of freeing or draining the page_frags, where we would > + * not expect it to match or that are slowpath anyway. > + */ > + if (__builtin_constant_p(nr) && > + atomic_long_read(&page->pp_frag_count) == nr) > + return 0; > + > + ret = atomic_long_sub_return(nr, &page->pp_frag_count); > + WARN_ON(ret < 0); I worried about this WARN_ON() as it generates an 'ud2' instruction which influence I-cache fetching. But I have disassembled (objdump) the page_pool.o binary and the ud2 gets placed last in the main function page_pool_put_page() that use this inlined function. Thus, I assume this is not a problem :-) > + return ret;