Re: [PATCH v3 2/3] powerpc: get hugetlbpage handling more generic
From: Scott Wood <oss@buserror.net>
Date: 2016-12-06 01:18:55
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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
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@@ -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