Messages in this thread | | | Subject | Re: [PATCH v3 2/3] powerpc: get hugetlbpage handling more generic | From | Christophe LEROY <> | Date | Wed, 7 Dec 2016 07:59:07 +0100 |
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Le 07/12/2016 à 02:06, Scott Wood a écrit : > On Tue, 2016-12-06 at 07:34 +0100, Christophe LEROY wrote: >> >> Le 06/12/2016 à 02:18, Scott Wood a écrit : >>> >>> 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. >> Ok, I'll check it again, I was expecting it to still work properly on >> book3e, because after applying patch 3 it works properly on the 8xx. > > On 8xx you probably happen to have a page size that yields "pdshift <= shift" > even with the incorrect pdshift calculation, causing hugepte_cache to be > allocated. The smallest hugepage size on 8xx is 512k compared to 4M on fsl- > book3e. >
Indeed it works because on 8xx, PUD_SHIFT == PMD_SHIFT == PGDIR_SHIFT
Christophe
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