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Message-ID: <46939efe-cf79-4dcd-9e47-9340956feb03@arm.com>
Date: Tue, 17 Dec 2024 06:53:22 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: Dev Jain <dev.jain@....com>, akpm@...ux-foundation.org, david@...hat.com,
willy@...radead.org, kirill.shutemov@...ux.intel.com
Cc: anshuman.khandual@....com, catalin.marinas@....com, cl@...two.org,
vbabka@...e.cz, mhocko@...e.com, apopple@...dia.com,
dave.hansen@...ux.intel.com, will@...nel.org, baohua@...nel.org,
jack@...e.cz, srivatsa@...il.mit.edu, haowenchao22@...il.com,
hughd@...gle.com, aneesh.kumar@...nel.org, yang@...amperecomputing.com,
peterx@...hat.com, ioworker0@...il.com, wangkefeng.wang@...wei.com,
ziy@...dia.com, jglisse@...gle.com, surenb@...gle.com,
vishal.moola@...il.com, zokeefe@...gle.com, zhengqi.arch@...edance.com,
jhubbard@...dia.com, 21cnbao@...il.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 02/12] khugepaged: Generalize alloc_charge_folio()
On 16/12/2024 16:50, Dev Jain wrote:
> Pass order to alloc_charge_folio() and update mTHP statistics.
>
> Signed-off-by: Dev Jain <dev.jain@....com>
> ---
> include/linux/huge_mm.h | 2 ++
> mm/huge_memory.c | 4 ++++
> mm/khugepaged.c | 13 +++++++++----
> 3 files changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 93e509b6c00e..8b6d0fed99b3 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -119,6 +119,8 @@ enum mthp_stat_item {
> MTHP_STAT_ANON_FAULT_ALLOC,
> MTHP_STAT_ANON_FAULT_FALLBACK,
> MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
> + MTHP_STAT_ANON_COLLAPSE_ALLOC,
> + MTHP_STAT_ANON_COLLAPSE_ALLOC_FAILED,
> MTHP_STAT_ZSWPOUT,
> MTHP_STAT_SWPIN,
> MTHP_STAT_SWPIN_FALLBACK,
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 2da5520bfe24..2e582fad4c77 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -615,6 +615,8 @@ static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> DEFINE_MTHP_STAT_ATTR(anon_fault_alloc, MTHP_STAT_ANON_FAULT_ALLOC);
> DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK);
> DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
> +DEFINE_MTHP_STAT_ATTR(anon_collapse_alloc, MTHP_STAT_ANON_COLLAPSE_ALLOC);
> +DEFINE_MTHP_STAT_ATTR(anon_collapse_alloc_failed, MTHP_STAT_ANON_COLLAPSE_ALLOC_FAILED);
> DEFINE_MTHP_STAT_ATTR(zswpout, MTHP_STAT_ZSWPOUT);
> DEFINE_MTHP_STAT_ATTR(swpin, MTHP_STAT_SWPIN);
> DEFINE_MTHP_STAT_ATTR(swpin_fallback, MTHP_STAT_SWPIN_FALLBACK);
> @@ -636,6 +638,8 @@ static struct attribute *anon_stats_attrs[] = {
> &anon_fault_alloc_attr.attr,
> &anon_fault_fallback_attr.attr,
> &anon_fault_fallback_charge_attr.attr,
> + &anon_collapse_alloc_attr.attr,
> + &anon_collapse_alloc_failed_attr.attr,
> #ifndef CONFIG_SHMEM
> &zswpout_attr.attr,
> &swpin_attr.attr,
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 95643e6e5f31..02cd424b8e48 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1073,21 +1073,26 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
> }
>
> static int alloc_charge_folio(struct folio **foliop, struct mm_struct *mm,
> - struct collapse_control *cc)
> + int order, struct collapse_control *cc)
> {
> gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
> GFP_TRANSHUGE);
> int node = hpage_collapse_find_target_node(cc);
> struct folio *folio;
>
> - folio = __folio_alloc(gfp, HPAGE_PMD_ORDER, node, &cc->alloc_nmask);
> + folio = __folio_alloc(gfp, order, node, &cc->alloc_nmask);
> if (!folio) {
> *foliop = NULL;
> count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
> + if (order != HPAGE_PMD_ORDER)
> + count_mthp_stat(order, MTHP_STAT_ANON_COLLAPSE_ALLOC_FAILED);
Bug? We should be calling count_mthp_stat() for all orders, but only calling
count_vm_event(THP_*) for PMD_ORDER, as per pattern laid out by other mTHP stats.
The aim is for existing THP stats (which are implicitly only counting PMD-sized
THP) to continue only to count PMD-sized THP. It's a userspace ABI and we were
scared of the potential to break things if we changed the existing counters'
semantics.
> return SCAN_ALLOC_HUGE_PAGE_FAIL;
> }
>
> count_vm_event(THP_COLLAPSE_ALLOC);
> + if (order != HPAGE_PMD_ORDER)
> + count_mthp_stat(order, MTHP_STAT_ANON_COLLAPSE_ALLOC);
Same problem.
Also, I agree with Baolin that we don't want "anon" in the title. This is a
generic path used for file-backed memory. So once you fix the bug, the new stats
will also be counting the file-backed memory too (although for now, only for
PMD_ORDER).
> +
> if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
> folio_put(folio);
> *foliop = NULL;
> @@ -1124,7 +1129,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
> */
> mmap_read_unlock(mm);
>
> - result = alloc_charge_folio(&folio, mm, cc);
> + result = alloc_charge_folio(&folio, mm, order, cc);
Where is order coming from? I'm guessing that's added later, so this patch won't
compile on it's own? Perhaps HPAGE_PMD_ORDER for now?
> if (result != SCAN_SUCCEED)
> goto out_nolock;
>
> @@ -1850,7 +1855,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
> VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
> VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
>
> - result = alloc_charge_folio(&new_folio, mm, cc);
> + result = alloc_charge_folio(&new_folio, mm, HPAGE_PMD_ORDER, cc);
> if (result != SCAN_SUCCEED)
> goto out;
>
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