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Date: Mon, 13 Feb 2017 12:24:07 +0000 From: Russell King - ARM Linux <linux@...linux.org.uk> To: Will Deacon <will.deacon@....com> Cc: zhouxianrong@...wei.com, mark.rutland@....com, wangkefeng.wang@...wei.com, srikar@...ux.vnet.ibm.com, Mi.Sophia.Wang@...wei.com, catalin.marinas@....com, linux-mm@...ck.org, zhangshiming5@...wei.com, frowand.list@...il.com, zijun_hu@....com, jszhang@...vell.com, won.ho.park@...wei.com, kuleshovmail@...il.com, devicetree@...r.kernel.org, chengang@...ndsoft.com.cn, zhouxiyu@...wei.com, tj@...nel.org, robh+dt@...nel.org, weidu.du@...wei.com, linux-arm-kernel@...ts.infradead.org, ard.biesheuvel@...aro.org, steve.capper@....com, linux-kernel@...r.kernel.org, joe@...ches.com, dennis.chen@....com, akpm@...ux-foundation.org, gkulkarni@...iumnetworks.com Subject: Re: [PATCH] mm: free reserved area's memmap if possiable On Mon, Feb 13, 2017 at 12:17:00PM +0000, Will Deacon wrote: > Adding linux-arm-kernel and devicetree (look for "raw-pfn"), since this > impacts directly on those. > > On Mon, Feb 13, 2017 at 08:02:29PM +0800, zhouxianrong@...wei.com wrote: > > From: zhouxianrong <zhouxianrong@...wei.com> > > > > just like freeing no-map area's memmap we could free reserved > > area's memmap as well only when user of reserved area indicate > > that we can do this in dts or drivers. that is, user of reserved > > area know how to use the reserved area who could not memblock_free > > or free_reserved_xxx the reserved area and regard the area as raw > > pfn usage. the patch supply a way to users who want to utilize the > > memmap memory corresponding to raw pfn reserved areas as many as > > possible. > > I don't really understand this. Can you point me at a specific use-case, > please? Is CMA involved here? You don't need "dt permission" to free the memmap page array for the regions between memory areas. In fact, adding a DT property for that goes against the "DT describes the hardware not the implementation" requirement, since the memmap page array is a Linux implementation detail. 32-bit ARM has been freeing the memmap page array between memory areas for years since pre-DT days, and continues to do so. See free_unused_memmap(). -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
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