Messages in this thread | | | Subject | Re: [PATCH v2 2/2] powerpc/mm: call H_BLOCK_REMOVE when supported | From | Laurent Dufour <> | Date | Thu, 19 Sep 2019 17:17:35 +0200 |
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Le 18/09/2019 à 15:42, Michael Ellerman a écrit : > Hi Laurent, > > Few comments ...
Hi Michael,
Thanks for the review and the nitpicking ;) > > Laurent Dufour <ldufour@linux.ibm.com> writes: >> Now we do not call _BLOCK_REMOVE all the time when the feature is >> exhibited. > > This isn't true until after the patch is applied, ie. the tense is > wrong. The rest of the change log explains things fine, so just drop > that sentence I think. > > Can you include the info about the oops in here. > >> Depending on the hardware and the hypervisor, the hcall H_BLOCK_REMOVE may >> not be able to process all the page size for a segment base page size, as > ^ > sizes >> reported by the TLB Invalidate Characteristics.o > ^ > stray "o" >> >> For each couple base segment page size and actual page size, this > ^ > "pair of" >> characteristic is telling the size of the block the hcall is supporting. > ^ ^ > "tells us" supports >> >> Due to the involve complexity in do_block_remove() and call_block_remove(), > ^ > "required" is better I think >> and the fact currently a 8 size block is returned by the hypervisor, we > ^ ^ > that "block of size 8" >> are only supporting 8 size block to the H_BLOCK_REMOVE hcall. >> >> Furthermore a warning message is displayed at boot time in the case of an >> unsupported block size. > > I'm not sure we should be doing that? It could be unnecessarily spammy. > >> In order to identify this limitation easily in the code,a local define >> HBLKR_SUPPORTED_SIZE defining the currently supported block size, and a >> dedicated checking helper is_supported_hlbkr() are introduced. >> >> For regular pages and hugetlb, the assumption is made that the page size is >> equal to the base page size. For THP the page size is assumed to be 16M. >> >> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com> >> --- >> arch/powerpc/platforms/pseries/lpar.c | 35 +++++++++++++++++++++++++-- >> 1 file changed, 33 insertions(+), 2 deletions(-) >> >> diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c >> index 98a5c2ff9a0b..e2ad9b3b1097 100644 >> --- a/arch/powerpc/platforms/pseries/lpar.c >> +++ b/arch/powerpc/platforms/pseries/lpar.c >> @@ -65,6 +65,13 @@ EXPORT_SYMBOL(plpar_hcall_norets); >> */ >> static int hblkr_size[MMU_PAGE_COUNT][MMU_PAGE_COUNT]; >> >> +/* >> + * Due to the involved complexity, and that the current hypervisor is only >> + * returning this value or 0, we are limiting the support of the H_BLOCK_REMOVE >> + * buffer size to 8 size block. >> + */ >> +#define HBLKR_SUPPORTED_BLOCK_SIZE 8 >> + >> #ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE >> static u8 dtl_mask = DTL_LOG_PREEMPT; >> #else >> @@ -993,6 +1000,15 @@ static void pSeries_lpar_hpte_invalidate(unsigned long slot, unsigned long vpn, >> #define HBLKR_CTRL_ERRNOTFOUND 0x8800000000000000UL >> #define HBLKR_CTRL_ERRBUSY 0xa000000000000000UL >> >> +/* >> + * Returned true if we are supporting this block size for the specified segment >> + * base page size and actual page size. >> + */ >> +static inline bool is_supported_hlbkr(int bpsize, int psize) >> +{ >> + return (hblkr_size[bpsize][psize] == HBLKR_SUPPORTED_BLOCK_SIZE); >> +} >> + >> /** >> * H_BLOCK_REMOVE caller. >> * @idx should point to the latest @param entry set with a PTEX. >> @@ -1152,7 +1168,11 @@ static inline void __pSeries_lpar_hugepage_invalidate(unsigned long *slot, >> if (lock_tlbie) >> spin_lock_irqsave(&pSeries_lpar_tlbie_lock, flags); >> >> - if (firmware_has_feature(FW_FEATURE_BLOCK_REMOVE)) >> + /* >> + * Assuming THP size is 16M, and we only support 8 bytes size buffer >> + * for the momment. >> + */ >> + if (is_supported_hlbkr(psize, MMU_PAGE_16M)) > > It's not very clear that this is correct in all cases. ie. how do we > know we're being called for THP and not regular huge page? > > I think we're only called via: > flush_hash_hugepage() > -> mmu_hash_ops.hugepage_invalidate() > pSeries_lpar_hugepage_invalidate() > -> __pSeries_lpar_hugepage_invalidate() > > And flush_hash_hugepage() is called via: > __hash_page_thp() > and > hpte_do_hugepage_flush() > > The first is presumably fine, the 2nd is called in a few places: > __flush_hash_table_range() under if (is_thp) > hash__pmd_hugepage_update() > > > But it's a little bit fragile if the code ever evolves. Not sure if > there's a better solution, other than just documenting it.
Indeed __pSeries_lpar_hugepage_invalidate() can only be called for THP. flush_hash_hugepage() and hpte_do_hugepage_flush() are only defined (or valid) with CONFIG_TRANSPARENT_HUGEPAGE.
As Aneesh remind me, "hugepage" stands for THP.
> >> hugepage_block_invalidate(slot, vpn, count, psize, ssize); >> else >> hugepage_bulk_invalidate(slot, vpn, count, psize, ssize); >> @@ -1437,6 +1457,14 @@ void __init pseries_lpar_read_hblkr_characteristics(void) >> >> block_size = 1 << block_size; >> >> + /* >> + * If the block size is not supported by the kernel, report it, >> + * but continue reading the values, and the following blocks. >> + */ >> + if (block_size != HBLKR_SUPPORTED_BLOCK_SIZE) >> + pr_warn("Unsupported H_BLOCK_REMOVE block size : %d\n", >> + block_size); > > Does this need a printk? I'm worried it could end up triggering and > scaring people unnecessarily.
I agree, will remove.
> >> + >> for (npsize = local_buffer[idx++]; npsize > 0; npsize--) >> check_lp_set_hblk((unsigned int) local_buffer[idx++], >> block_size); >> @@ -1468,7 +1496,10 @@ static void pSeries_lpar_flush_hash_range(unsigned long number, int local) >> if (lock_tlbie) >> spin_lock_irqsave(&pSeries_lpar_tlbie_lock, flags); >> >> - if (firmware_has_feature(FW_FEATURE_BLOCK_REMOVE)) { >> + /* >> + * Currently, we only support 8 bytes size buffer in do_block_remove(). >> + */ >> + if (is_supported_hlbkr(batch->psize, batch->psize)) { >> do_block_remove(number, batch, param); >> goto out; >> } >> -- >> 2.23.0 > > cheers >
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