From: Matthew Wilcox <willy@infradead.org>
To: Song Liu <songliubraving@fb.com>
Cc: "William Kucharski" <william.kucharski@oracle.com>,
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Subject: Re: [PATCH v2 1/2] mm: Allow the page cache to allocate large pages
Date: Tue, 30 Jul 2019 13:26:32 -0700 [thread overview]
Message-ID: <20190730202632.GC4700@bombadil.infradead.org> (raw)
In-Reply-To: <443BA74D-9A8E-479B-9E63-4ACD6D6C0AF9@fb.com>
On Mon, Jul 29, 2019 at 10:03:40PM +0000, Song Liu wrote:
> > +/* If you add more flags, increment FGP_ORDER_SHIFT */
> > +#define FGP_ORDER_SHIFT 7
> > +#define FGP_PMD ((PMD_SHIFT - PAGE_SHIFT) << FGP_ORDER_SHIFT)
> > +#define FGP_PUD ((PUD_SHIFT - PAGE_SHIFT) << FGP_ORDER_SHIFT)
> > +#define fgp_get_order(fgp) ((fgp) >> FGP_ORDER_SHIFT)
>
> This looks like we want support order up to 25 (32 - 7). I guess we don't
> need that many. How about we specify the highest order to support here?
We can support all the way up to order 64 with just 6 bits, leaving 32 -
6 - 7 = 19 bits free. We haven't been adding FGP flags very quickly,
so I doubt we'll need anything larger.
> Also, fgp_flags is signed int, so we need to make sure fgp_flags is not
> negative.
If we ever get there, I expect people to convert the parameter from signed
int to unsigned long.
next prev parent reply other threads:[~2019-07-30 20:26 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-29 21:09 [PATCH v2 0/2] mm,thp: Add filemap_huge_fault() for THP William Kucharski
2019-07-29 21:09 ` [PATCH v2 1/2] mm: Allow the page cache to allocate large pages William Kucharski
2019-07-29 22:03 ` Song Liu
2019-07-30 20:26 ` Matthew Wilcox [this message]
2019-07-30 21:13 ` Song Liu
2019-07-29 21:09 ` [PATCH v2 2/2] mm,thp: Add experimental config option RO_EXEC_FILEMAP_HUGE_FAULT_THP William Kucharski
2019-07-29 22:47 ` Dan Williams
2019-07-30 19:18 ` Matthew Wilcox
2019-07-29 22:51 ` Song Liu
2019-07-30 14:11 ` William Kucharski
2019-07-30 19:14 ` Song Liu
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