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Message-ID: <20170807133107.GA16616@redhat.com> Date: Mon, 7 Aug 2017 09:31:07 -0400 From: Jerome Glisse <jglisse@...hat.com> To: Igor Stoppa <igor.stoppa@...wei.com> Cc: Michal Hocko <mhocko@...nel.org>, Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, linux-security-module@...r.kernel.org, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Kees Cook <keescook@...gle.com> Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator On Mon, Aug 07, 2017 at 02:26:21PM +0300, Igor Stoppa wrote: > On 04/08/17 11:12, Michal Hocko wrote: > > On Fri 04-08-17 11:02:46, Igor Stoppa wrote: > > [...] > > >> struct page { > >> /* First double word block */ > >> unsigned long flags; /* Atomic flags, some possibly > >> * updated asynchronously */ > >> union { > >> struct address_space *mapping; /* If low bit clear, points to > >> * inode address_space, or NULL. > >> * If page mapped as anonymous > >> * memory, low bit is set, and > >> * it points to anon_vma object: > >> * see PAGE_MAPPING_ANON below. > >> */ > >> ... > >> } > >> > >> mapping seems to be used exclusively in 2 ways, based on the value of > >> its lower bit. > > > > Not really. The above applies to LRU pages. Please note that Slab pages > > use s_mem and huge pages use compound_mapcount. If vmalloc pages are > > using none of those already you can add a new field there. > > Yes, both from reading the code and some experimentation, it seems that > vmalloc is not using either field. > > I'll add a vm_area field as you advised. > > Is this something I could send as standalone patch? Note that vmalloc() is not the only thing that use vmalloc address space. There is also vmap() and i know one set of drivers that use vmap() and also use the mapping field of struct page namely GPU drivers. So like i said previously i would store a flag inside vm_struct to know if page you are looking at are pmalloc or not. Again do you need to store something per page ? Would storing it per vm_struct not be enough ? Cheers, Jérôme
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