From: Huaisheng HS1 Ye <yehs1@lenovo.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"mhocko@suse.com" <mhocko@suse.com>,
"vbabka@suse.cz" <vbabka@suse.cz>,
"mgorman@techsingularity.net" <mgorman@techsingularity.net>,
"alexander.levin@verizon.com" <alexander.levin@verizon.com>,
"colyli@suse.de" <colyli@suse.de>,
NingTing Cheng <chengnt@lenovo.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [External] Re: [PATCH v1] include/linux/gfp.h: getting rid of GFP_ZONE_TABLE/BAD
Date: Fri, 18 May 2018 03:03:35 +0000 [thread overview]
Message-ID: <HK2PR03MB1684A5EE7432CAF9763608D992900@HK2PR03MB1684.apcprd03.prod.outlook.com> (raw)
In-Reply-To: <20180511132613.GA30263@bombadil.infradead.org>
> From: Matthew Wilcox [mailto:willy@infradead.org]
> Sent: Friday, May 11, 2018 9:26 PM
> On Fri, May 11, 2018 at 03:24:34AM +0000, Huaisheng HS1 Ye wrote:
> > > From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On Behalf Of
> Matthew
> > > Wilcox
> > > On Fri, May 11, 2018 at 12:10:25AM +0800, Huaisheng Ye wrote:
> > > > -#define __GFP_DMA ((__force gfp_t)___GFP_DMA)
> > > > -#define __GFP_HIGHMEM ((__force gfp_t)___GFP_HIGHMEM)
> > > > -#define __GFP_DMA32 ((__force gfp_t)___GFP_DMA32)
> > > > +#define __GFP_DMA ((__force gfp_t)OPT_ZONE_DMA ^ ZONE_NORMAL)
> > > > +#define __GFP_HIGHMEM ((__force gfp_t)ZONE_MOVABLE ^ ZONE_NORMAL)
> > > > +#define __GFP_DMA32 ((__force gfp_t)OPT_ZONE_DMA32 ^ ZONE_NORMAL)
> > >
> > > No, you've made gfp_zone even more complex than it already is.
> > > If you can't use OPT_ZONE_HIGHMEM here, then this is a waste of time.
> > >
> > Dear Matthew,
> >
> > The reason why I don't use OPT_ZONE_HIGHMEM for __GFP_HIGHMEM directly is that,
> for x86_64 platform there is no CONFIG_HIGHMEM, so OPT_ZONE_HIGHMEM shall always be
> equal to ZONE_NORMAL.
>
> Right. On 64-bit platforms, if somebody asks for HIGHMEM, they should
> get NORMAL pages.
>
> > For gfp_zone it is impossible to distinguish the meaning of lowest 3 bits in flags.
> How can gfp_zone to understand it comes from OPT_ZONE_HIGHMEM or ZONE_NORMAL?
> > And the most pained thing is that, if __GFP_HIGHMEM with movable flag enabled, it
> means that ZONE_MOVABLE shall be returned.
> > That is different from ZONE_DMA, ZONE_DMA32 and ZONE_NORMAL.
>
> The point of this exercise is to actually encode the zone number in
> the bottom bits of the GFP flags instead of something which has to be
> interpreted into a zone number. When somebody sets __GFP_MOVABLE, they
> should also be setting ZONE_MOVABLE:
>
> -#define __GFP_MOVABLE ((__force gfp_t)___GFP_MOVABLE) /* ZONE_MOVABLE allowed */
> +#define __GFP_MOVABLE ((__force gfp_t)(___GFP_MOVABLE | (ZONE_MOVABLE ^ ZONE_NORMAL)))
>
> One thing that does need to change is:
>
> -#define GFP_HIGHUSER_MOVABLE (GFP_HIGHUSER | __GFP_MOVABLE)
> +#define GFP_HIGHUSER_MOVABLE (GFP_USER | __GFP_MOVABLE)
>
> otherwise we'll be OR'ing ZONE_MOVABLE and ZONE_HIGHMEM together.
Dear Matthew,
After thinking it over and over, I am afraid there is something needs to be discussed here.
You know current X86_64 config file of kernel doesn't enable CONFIG_HIGHMEM, that is to say from this below,
#define __GFP_HIGHMEM ((__force gfp_t)OPT_ZONE_HIGHMEM ^ ZONE_NORMAL)
__GFP_HIGHMEM should equal to 0b0000, same as the value of ZONE_NORMAL gets encoded.
If we define __GFP_MOVABLE like this,
#define __GFP_MOVABLE ((__force gfp_t)(___GFP_MOVABLE | (ZONE_MOVABLE ^ ZONE_NORMAL)))
Just like your introduced before, with this modification when somebody sets __GFP_MOVABLE, they should also be setting ZONE_MOVABLE.
That brings us a problem, current mm (GFP_ZONE_TABLE) treats __GFP_MOVABLE as ZONE_NORMAL with movable policy, if without __GFP_HIGHMEM.
The mm shall allocate a page or pages from migrate movable list of ZONE_NORMAL's freelist.
So that conflicts with this modification. And I have checked current kernel, some of function directly set parameter gfp like this.
For example, in fs/ext4/extents.c __read_extent_tree_block,
bh = sb_getblk_gfp(inode->i_sb, pblk, __GFP_MOVABLE | GFP_NOFS);
for these situations, I think only modify GFP_HIGHUSER_MOVABLE is not enough. I am preparing a workaround to solve this in the V2 patch.
Later I will upload it to email loop.
Sincerely,
Huaisheng Ye
> > I was thinking...
> > Whether it is possible to use other judgement condition to decide OPT_ZONE_HIGHMEM
> or ZONE_MOVABLE shall be returned from gfp_zone.
> >
> > Sincerely,
> > Huaisheng Ye
> >
> >
> > > > static inline enum zone_type gfp_zone(gfp_t flags)
> > > > {
> > > > enum zone_type z;
> > > > - int bit = (__force int) (flags & GFP_ZONEMASK);
> > > > + z = ((__force unsigned int)flags & ___GFP_ZONE_MASK) ^ ZONE_NORMAL;
> > > > +
> > > > + if (z > OPT_ZONE_HIGHMEM)
> > > > + z = OPT_ZONE_HIGHMEM +
> > > > + !!((__force unsigned int)flags & ___GFP_MOVABLE);
> > > >
> > > > - z = (GFP_ZONE_TABLE >> (bit * GFP_ZONES_SHIFT)) &
> > > > - ((1 << GFP_ZONES_SHIFT) - 1);
> > > > - VM_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
> > > > + VM_BUG_ON(z > ZONE_MOVABLE);
> > > > return z;
> > > > }
> >
prev parent reply other threads:[~2018-05-18 3:04 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1525968625-40825-1-git-send-email-yehs1@lenovo.com>
2018-05-10 16:30 ` [PATCH v1] include/linux/gfp.h: getting rid of GFP_ZONE_TABLE/BAD Matthew Wilcox
2018-05-11 3:24 ` [External] " Huaisheng HS1 Ye
2018-05-11 13:26 ` Matthew Wilcox
2018-05-12 11:35 ` Huaisheng HS1 Ye
2018-05-12 14:22 ` Matthew Wilcox
2018-05-16 12:12 ` Huaisheng HS1 Ye
2018-05-18 3:03 ` Huaisheng HS1 Ye [this message]
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