From: Scott Wood <oss@buserror•net>
To: Christophe Leroy <christophe.leroy@c-s•fr>,
Benjamin Herrenschmidt <benh@kernel•crashing.org>,
Paul Mackerras <paulus@samba•org>,
Michael Ellerman <mpe@ellerman•id.au>
Cc: linux-kernel@vger•kernel.org, linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH v3 2/3] powerpc: get hugetlbpage handling more generic
Date: Mon, 05 Dec 2016 19:18:36 -0600 [thread overview]
Message-ID: <1480987116.32531.17.camel@buserror.net> (raw)
In-Reply-To: <69b1226ce134761fd7ab81a498bdb85cd737280f.1474441302.git.christophe.leroy@c-s.fr>
On Wed, 2016-09-21 at 10:11 +0200, Christophe Leroy wrote:
> Today there are two implementations of hugetlbpages which are managed
> by exclusive #ifdefs:
> * FSL_BOOKE: several directory entries points to the same single hugepage
> * BOOK3S: one upper level directory entry points to a table of hugepages
>
> In preparation of implementation of hugepage support on the 8xx, we
> need a mix of the two above solutions, because the 8xx needs both cases
> depending on the size of pages:
> * In 4k page size mode, each PGD entry covers a 4M bytes area. It means
> that 2 PGD entries will be necessary to cover an 8M hugepage while a
> single PGD entry will cover 8x 512k hugepages.
> * In 16 page size mode, each PGD entry covers a 64M bytes area. It means
> that 8x 8M hugepages will be covered by one PGD entry and 64x 512k
> hugepages will be covers by one PGD entry.
>
> This patch:
> * removes #ifdefs in favor of if/else based on the range sizes
> * merges the two huge_pte_alloc() functions as they are pretty similar
> * merges the two hugetlbpage_init() functions as they are pretty similar
[snip]
> @@ -860,16 +803,34 @@ static int __init hugetlbpage_init(void)
> * if we have pdshift and shift value same, we don't
> * use pgt cache for hugepd.
> */
> - if (pdshift != shift) {
> + if (pdshift > shift) {
> pgtable_cache_add(pdshift - shift, NULL);
> if (!PGT_CACHE(pdshift - shift))
> panic("hugetlbpage_init(): could not create
> "
> "pgtable cache for %d bit
> pagesize\n", shift);
> }
> +#ifdef CONFIG_PPC_FSL_BOOK3E
> + else if (!hugepte_cache) {
This else never triggers on book3e, because the way this function calculates
pdshift is wrong for book3e (it uses PyD_SHIFT instead of HUGEPD_PxD_SHIFT).
We later get OOMs because huge_pte_alloc() calculates pdshift correctly,
tries to use hugepte_cache, and fails.
If the point of this patch is to remove the compile-time decision on whether
to do things the book3e way, why are there still ifdefs such as the ones
controlling the definition of HUGEPD_PxD_SHIFT? How does what you're doing on
8xx (for certain page sizes) differ from book3e?
-Scott
next prev parent reply other threads:[~2016-12-06 1:18 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-21 8:11 [PATCH v3 0/3] powerpc: implementation of huge pages for 8xx Christophe Leroy
2016-09-21 8:11 ` [PATCH v3 1/3] powerpc: port 64 bits pgtable_cache to 32 bits Christophe Leroy
2016-09-22 7:27 ` Aneesh Kumar K.V
2016-09-21 8:11 ` [PATCH v3 2/3] powerpc: get hugetlbpage handling more generic Christophe Leroy
2016-09-21 16:58 ` Aneesh Kumar K.V
2016-11-24 5:23 ` [v3,2/3] " Scott Wood
2016-11-25 8:14 ` Christophe LEROY
2016-12-05 2:58 ` Scott Wood
2016-12-06 1:18 ` Scott Wood [this message]
2016-12-06 6:34 ` [PATCH v3 2/3] " Christophe LEROY
2016-12-07 1:06 ` Scott Wood
2016-12-07 6:59 ` Christophe LEROY
2016-09-21 8:11 ` [PATCH v3 3/3] powerpc/8xx: Implement support of hugepages Christophe Leroy
2016-09-21 16:58 ` Aneesh Kumar K.V
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