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From:   Song Liu <song@kernel.org>
Date:   Fri, 19 May 2023 08:08:54 -0700
Message-ID: <CAPhsuW7_hb9T-uuB2FuXYMs7WA_XMbV809zOPSV7eOQeh4k3Qw@mail.gmail.com>
Subject: Re: [RFC PATCH 1/5] mm: intorduce __GFP_UNMAPPED and unmapped_alloc()
To:     Kent Overstreet <kent.overstreet@linux.dev>
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
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On Thu, May 18, 2023 at 6:24=E2=80=AFPM Kent Overstreet
<kent.overstreet@linux.dev> wrote:
>
> 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 th=
en
> > use it for many small allocations. IIUC, buddy allocator will use unall=
ocated
> > 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.

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