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bh=SVWWSvjsAAyEzqQR/A/gO5W9iuwYkJ4nSovwV47+0uk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=HYXfx1SQhw0AmoHz5uP6xzwI0wXN7BZnMxVu7zuJRoTIbYkejxwH9Xs1ISqr19wpx X3fiNsirE6Q1n6BwF58x0f47S5o2kQS3fOGxfR2z4zI64PDMM7sB89khmwEPQy6iqu OIe9a8ZyzyDY1d3zxK59+Kk9b/cKSzTCavw9ClEs= Date: Thu, 12 Jan 2023 13:29:57 -0800 From: Andrew Morton To: Pasha Tatashin Cc: mhocko@suse.com, vbabka@suse.cz, david@redhat.com, quic_charante@quicinc.com, lizhe.67@bytedance.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2] mm/page_ext: Do not allocate space for page_ext->flags if not needed Message-Id: <20230112132957.6cb97c2afad17cdeb06fcd10@linux-foundation.org> In-Reply-To: <20230112153348.3202173-1-pasha.tatashin@soleen.com> References: <20230112153348.3202173-1-pasha.tatashin@soleen.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B22E4140018 X-Rspam-User: X-Stat-Signature: quh1efx37kj543hd9974yw41be4ytp73 X-HE-Tag: 1673559000-595900 X-HE-Meta: U2FsdGVkX1+KVhNbqCNRoK/50zyci9ao3gOJRrpV+cvDZ4Jkk54ZIVgr3YgrhJ+2d5rBwFKmm3YMbzbCGViCCCz+FMbF4l/fBDEht/A6FjAytrC3LdwgppYcr+hgYNapI7j/3hBU09NOib6/0ddcpRqXZfBKnSMLXViw8NMvFpFDZFwHIJbtMNRPHTtDV+SfoKKPvd9Dp5OTtCiwA+LTQ+CWFD6PyhYML48KfJwNbSE3PbVxYbThjfzFBI40+jNIjhOmsRRI6Xh8hSEayFW8Ku7YPidmBvxnEJBQmryW7QYC1/FlOcGHrkYEQdAQqc2OJXGEl1W9E2mvG8HAeaQ+xLpzdortPmGhUCgRmpIyBGLj+EpEcaW6IiAdHy8Y1yRBeOvN1rCnzxyHYykmytV6kqkVOHL0fq8B15IyW/2SOe1gFiHeFsO+YD6gRSi1fhgUhTITHqg5fNG/uU0l/e8HL5o5HEHL8+uIYMRU//ZYovwuccKzsO2H9EL90iXd2Hj1Xzpj8BWGoZ/yJr/3z/Q0KmrN5XJtfVJK7T4gzjOz+kOpcPyPe5B43sj9ScHYxtgHMsQuqdOxTsONB9iFSiOwATxH5OZHricQ3szZriUbfZOWEeYfbs1TV+Pusm5qzIg2T5NgmWVhRazP+J89SkZZqBcOUKIEXrBXTNl0GB+wJ5EmeJnvuah+SgtvdZjqObgg6DNTsFfuCfLOPiEhmkViyl8IgVQ+ay4mglfC3oZkoQll74t7tmQ27zOWH3UiJ3Bvi96sca7wtTz2Bq7FMywJtcJbOsnStb/NSiD8U/vRIms7k+rUy/TyKObpDqMS4I9TxTdInzf7fS2yFdqkW5G3gm2N1GdgetPXX9N+9E5qyFeWuJp7fmQ8D5Pfentk7bVEVcB8DbwvSE89TUimzf59ogfAGHfLBXU149YdBLLBMyfr3lWGoJ4LIEo4B1sqyUHUU1ttVa6ENN2u6+rfA+p /y3454YZ Hhf2gHbi3ktiVUBPbCe7EsO3pBZYvhS6rSxGtoX+otbLNf8vL2n8RFlhq8UN//mfB6Ez/2e2cy42PBJPxIw+bwiLCCSjmWc3eevqS9lXR3ZpGJZS9jeaLA3gJlg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 12 Jan 2023 15:33:48 +0000 Pasha Tatashin wrote: > There is 8 byte page_ext->flags field allocated per page whenever > CONFIG_PAGE_EXTENSION is enabled. However, not every user of page_ext > uses flags. Therefore, check whether flags is needed at least by one > user and if so allocate space for it. > > For example when page_table_check is enabled, on a machine with 128G > of memory before the fix: > > [ 2.244288] allocated 536870912 bytes of page_ext > after the fix: > [ 2.160154] allocated 268435456 bytes of page_ext > Looks nice. Does it work correctly with early_page_ext=1? > --- a/include/linux/page_ext.h > +++ b/include/linux/page_ext.h > @@ -12,10 +12,14 @@ struct page_ext_operations { > size_t size; > bool (*need)(void); > void (*init)(void); > + bool using_shared_ext_flags; > }; Seems overly complicated. Can we change the three early-init functions such as setup_early_page_ext() to simply set some global bool flag? > #endif > }; > > -unsigned long page_ext_size = sizeof(struct page_ext); > +unsigned long page_ext_size; > > static unsigned long total_usage; > static struct page_ext *lookup_page_ext(const struct page *page); > @@ -105,6 +106,15 @@ static bool __init invoke_need_callbacks(void) > int entries = ARRAY_SIZE(page_ext_ops); > bool need = false; > > + for (i = 0; i < entries; i++) { > + if (page_ext_ops[i]->need && page_ext_ops[i]->need()) { I don't think this (or the below) need to check for ->need==NULL? > + if (page_ext_ops[i]->using_shared_ext_flags) { > + page_ext_size = sizeof(struct page_ext); > + break; > + } > + } > + } > + > for (i = 0; i < entries; i++) { > if (page_ext_ops[i]->need && page_ext_ops[i]->need()) { > page_ext_ops[i]->offset = page_ext_size;