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Message-ID: <87y2ylvhyo.fsf@mpe.ellerman.id.au>
Date: Wed, 18 Sep 2019 23:42:39 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Laurent Dufour <ldufour@...ux.ibm.com>, benh@...nel.crashing.org,
paulus@...ba.org, aneesh.kumar@...ux.ibm.com, npiggin@...il.com,
linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] powerpc/mm: call H_BLOCK_REMOVE when supported
Hi Laurent,
Few comments ...
Laurent Dufour <ldufour@...ux.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@...ux.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.
> 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.
> +
> 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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