linux-kernel - Re: [PATCH 4/4] x86/mm: replace GFP_ATOMIC with GFP

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Message-ID: <29f9155d0d164d349784b4c40cd806bc1129005d.camel@intel.com>
Date:   Fri, 12 Nov 2021 22:39:11 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "rppt@...nel.org" <rppt@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rppt@...ux.ibm.com" <rppt@...ux.ibm.com>,
        "Lutomirski, Andy" <luto@...nel.org>, "bp@...en8.de" <bp@...en8.de>
Subject: Re: [PATCH 4/4] x86/mm: replace GFP_ATOMIC with GFP_KERNEL for direct
 map allocations

On Fri, 2021-11-12 at 14:30 +0200, Mike Rapoport wrote:
> The fixmap is less 2M so all the page tables will be allocated from
> gpt
> cache/memblock so __set_fixmap() will be essentially a call to
> set_pte().

If you configure CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP it can be larger.

> 
> I'll see how to ensure that page tables for ghex fixmaps are
> explicitly
> preallocated at init time.
>  

Investigating a bit further, fixmap pte's are allocated statically with
level1_fixmap_pgt, so set_fixmap() should never call spp_getpage() pre
or post after_bootmem. So I guess GFP_KERNEL shouldn't come into play
for all the fixmap callers.

Thanks!

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>