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From: Joerg Roedel <jroedel@suse.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Joerg Roedel <joro@8bytes.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	stable <stable@vger.kernel.org>,
	Chris Wilson <chris@chris-wilson.co.uk>,
	Linux-MM <linux-mm@kvack.org>,
	David Vrabel <david.vrabel@citrix.com>,
	Pavel Machek <pavel@ucw.cz>, Dave Airlie <airlied@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	intel-gfx <intel-gfx@lists.freedesktop.org>
Subject: Re: [Intel-gfx] [PATCH v2] mm: Track page table modifications in __apply_to_page_range()
Date: Sat, 22 Aug 2020 18:12:58 +0200	[thread overview]
Message-ID: <20200822161258.GP3354@suse.de> (raw)
In-Reply-To: <CAHk-=wgNEsVwVMwQdHL4O1tDWQa-HcmOv-EmqLTQH+SoC2CkWA@mail.gmail.com>

On Fri, Aug 21, 2020 at 12:18:41PM -0700, Linus Torvalds wrote:
> It also strikes me that I think the only architecture that uses the
> whole arch_sync_kernel_mappings() thing is now just x86-32.
> 
> [ Well, x86-64 still has it, but that's because we undid the 64-bit
> removal, but it's on the verge of going away and x86-64 shouldn't
> actually _need_ it any more ]
> 
> So all of this seems to be purely for 32-bit x86. Which kind of makes
> this all fail the smell test.

Yeah, it is certainly not the nicest thing to have in generic mm code,
but at least it is an improvement of the vmalloc_sync_all() interface we
had before, where the function had to be called at random undefined
places.

And x86-32 needs it, as long as we have the !SHARED_KERNEL_PMD cases
(which includes legacy paging). Or we also pre-allocate the PMDs on
x86-32 and forbid large ioremap mappings. But since the vmalloc area
gets larger with less RAM on x86-32, this would penalize low memory
machines by using more pages for the pre-allocations.

Not sure if making the vmalloc area on x86-32 a fixed 128MB range of
address space independent of RAM size is doable or if it will break some
machines. But with that pre-allocating PMDs would make more sense and we
could get rid of the p?d_alloc_track() stuff.

Regards,

	Joerg
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

WARNING: multiple messages have this Message-ID (diff)
From: Joerg Roedel <jroedel@suse.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Joerg Roedel <joro@8bytes.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux-MM <linux-mm@kvack.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Chris Wilson <chris@chris-wilson.co.uk>,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	Pavel Machek <pavel@ucw.cz>, Dave Airlie <airlied@redhat.com>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>,
	David Vrabel <david.vrabel@citrix.com>,
	stable <stable@vger.kernel.org>
Subject: Re: [PATCH v2] mm: Track page table modifications in __apply_to_page_range()
Date: Sat, 22 Aug 2020 18:12:58 +0200	[thread overview]
Message-ID: <20200822161258.GP3354@suse.de> (raw)
In-Reply-To: <CAHk-=wgNEsVwVMwQdHL4O1tDWQa-HcmOv-EmqLTQH+SoC2CkWA@mail.gmail.com>

On Fri, Aug 21, 2020 at 12:18:41PM -0700, Linus Torvalds wrote:
> It also strikes me that I think the only architecture that uses the
> whole arch_sync_kernel_mappings() thing is now just x86-32.
> 
> [ Well, x86-64 still has it, but that's because we undid the 64-bit
> removal, but it's on the verge of going away and x86-64 shouldn't
> actually _need_ it any more ]
> 
> So all of this seems to be purely for 32-bit x86. Which kind of makes
> this all fail the smell test.

Yeah, it is certainly not the nicest thing to have in generic mm code,
but at least it is an improvement of the vmalloc_sync_all() interface we
had before, where the function had to be called at random undefined
places.

And x86-32 needs it, as long as we have the !SHARED_KERNEL_PMD cases
(which includes legacy paging). Or we also pre-allocate the PMDs on
x86-32 and forbid large ioremap mappings. But since the vmalloc area
gets larger with less RAM on x86-32, this would penalize low memory
machines by using more pages for the pre-allocations.

Not sure if making the vmalloc area on x86-32 a fixed 128MB range of
address space independent of RAM size is doable or if it will break some
machines. But with that pre-allocating PMDs would make more sense and we
could get rid of the p?d_alloc_track() stuff.

Regards,

	Joerg


  reply	other threads:[~2020-08-22 16:13 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-21 12:37 [Intel-gfx] [PATCH v2] mm: Track page table modifications in __apply_to_page_range() Joerg Roedel
2020-08-21 12:37 ` Joerg Roedel
2020-08-21 13:30 ` [Intel-gfx] ✓ Fi.CI.BAT: success for " Patchwork
2020-08-21 16:39 ` [Intel-gfx] ✗ Fi.CI.IGT: failure " Patchwork
2020-08-21 18:51 ` [Intel-gfx] [PATCH v2] " Chris Wilson
2020-08-21 18:51   ` Chris Wilson
2020-08-21 19:18 ` [Intel-gfx] " Linus Torvalds
2020-08-21 19:18   ` Linus Torvalds
2020-08-22 16:12   ` Joerg Roedel [this message]
2020-08-22 16:12     ` Joerg Roedel
2020-08-21 20:35 ` [Intel-gfx] " Andrew Morton
2020-08-21 20:35   ` Andrew Morton
2020-08-21 20:50   ` [Intel-gfx] " Chris Wilson
2020-08-21 20:50     ` Chris Wilson
2020-08-21 21:29     ` [Intel-gfx] " Pavel Machek
2020-08-21 21:29       ` Pavel Machek
2020-08-22 21:25     ` [Intel-gfx] " Pavel Machek
2020-08-22 21:25       ` Pavel Machek
2020-08-21 22:34 ` [Intel-gfx] " Andrew Morton
2020-08-21 22:34   ` Andrew Morton
2020-08-21 23:39   ` [Intel-gfx] " Chris Wilson
2020-08-21 23:39     ` Chris Wilson
2020-08-22 11:31     ` [Intel-gfx] " Chris Wilson
2020-08-22 11:31       ` Chris Wilson
2020-08-22 16:20       ` [Intel-gfx] " Joerg Roedel
2020-08-22 16:20         ` Joerg Roedel
2020-08-23 10:44 ` [Intel-gfx] " Pavel Machek
2020-08-23 10:44   ` Pavel Machek

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