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From:   Kent Overstreet <kent.overstreet@linux.dev>
To:     Song Liu <song@kernel.org>
Cc:     Mike Rapoport <rppt@kernel.org>, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vlastimil Babka <vbabka@suse.cz>, linux-kernel@vger.kernel.org,
        x86@kernel.org
Subject: Re: [RFC PATCH 1/5] mm: intorduce __GFP_UNMAPPED and unmapped_alloc()
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On Thu, May 18, 2023 at 01:51:08PM -0700, Song Liu wrote:
 
> To allocate memory for text, we will allocate 2MiB, make it ROX, and then
> use it for many small allocations. IIUC, buddy allocator will use unallocated
> parts of this page for metadata. I guess this may be a problem, as the
> whole page is ROX now, and we have to use text_poke to write to it.

The standard kernel buddy allocator does _not_ store anything in the
page itself - because the page might be a highmem page.

That's also why I went with the bitmap for my slab allocator; standard
kernel slab allocator stores a freelist ptr in free objects.