On Thu, 21 Sep 2023 20:27:51 +0800 Jiexun Wang <[email protected]> wrote:
> Currently the madvise_cold_or_pageout_pte_range() function exhibits
> significant latency under memory pressure, which can be effectively
> reduced by adding cond_resched() within the loop.
>
> When the batch_count reaches SWAP_CLUSTER_MAX, we reschedule
> the task to ensure fairness and avoid long lock holding times.
>
> ...
>
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -354,6 +354,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> struct folio *folio = NULL;
> LIST_HEAD(folio_list);
> bool pageout_anon_only_filter;
> + unsigned int batch_count = 0;
>
> if (fatal_signal_pending(current))
> return -EINTR;
> @@ -433,6 +434,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> regular_folio:
> #endif
> tlb_change_page_size(tlb, PAGE_SIZE);
> +restart:
> start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
The handling of start_pte looks OK.
> if (!start_pte)
> return 0;
> @@ -441,6 +443,15 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> for (; addr < end; pte++, addr += PAGE_SIZE) {
> ptent = ptep_get(pte);
>
> + if (++batch_count == SWAP_CLUSTER_MAX) {
> + batch_count = 0;
> + if (need_resched()) {
> + pte_unmap_unlock(start_pte, ptl);
> + cond_resched();
> + goto restart;
> + }
> + }
> +
> if (pte_none(ptent))
> continue;
>
I think this patch looks OK, but would appreciate careful review from
others, please.
On (23/09/21 17:41), Andrew Morton wrote:
> > Currently the madvise_cold_or_pageout_pte_range() function exhibits
> > significant latency under memory pressure, which can be effectively
> > reduced by adding cond_resched() within the loop.
> >
> > When the batch_count reaches SWAP_CLUSTER_MAX, we reschedule
> > the task to ensure fairness and avoid long lock holding times.
> >
> > ...
> >
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -354,6 +354,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> > struct folio *folio = NULL;
> > LIST_HEAD(folio_list);
> > bool pageout_anon_only_filter;
> > + unsigned int batch_count = 0;
> >
> > if (fatal_signal_pending(current))
> > return -EINTR;
> > @@ -433,6 +434,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> > regular_folio:
> > #endif
> > tlb_change_page_size(tlb, PAGE_SIZE);
> > +restart:
> > start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
>
> The handling of start_pte looks OK.
>
> > if (!start_pte)
> > return 0;
> > @@ -441,6 +443,15 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> > for (; addr < end; pte++, addr += PAGE_SIZE) {
> > ptent = ptep_get(pte);
> >
> > + if (++batch_count == SWAP_CLUSTER_MAX) {
> > + batch_count = 0;
> > + if (need_resched()) {
> > + pte_unmap_unlock(start_pte, ptl);
Shouldn't it leave lazy MMU mode here?
---
diff --git a/mm/madvise.c b/mm/madvise.c
index 0f222d464254..127f0c7b69ac 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -451,6 +451,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
if (++batch_count == SWAP_CLUSTER_MAX) {
batch_count = 0;
if (need_resched()) {
+ arch_leave_lazy_mmu_mode();
pte_unmap_unlock(start_pte, ptl);
cond_resched();
goto restart;
We need to leave lazy MMU mode before unlocking.
Fixes: b2f557a21bc8 ("mm/madvise: add cond_resched() in madvise_cold_or_pageout_pte_range()")
Signed-off-by: Sergey Senozhatsky <[email protected]>
---
mm/madvise.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/mm/madvise.c b/mm/madvise.c
index 0f222d464254..127f0c7b69ac 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -451,6 +451,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
if (++batch_count == SWAP_CLUSTER_MAX) {
batch_count = 0;
if (need_resched()) {
+ arch_leave_lazy_mmu_mode();
pte_unmap_unlock(start_pte, ptl);
cond_resched();
goto restart;
--
2.43.0.429.g432eaa2c6b-goog
On Fri, 26 Jan 2024 12:25:48 +0900 Sergey Senozhatsky <[email protected]> wrote:
> We need to leave lazy MMU mode before unlocking.
What might be the userspace-visible effects of this?
> Fixes: b2f557a21bc8 ("mm/madvise: add cond_resched() in madvise_cold_or_pageout_pte_range()"
> Signed-off-by: Sergey Senozhatsky <[email protected]>
I'll add a cc:stable.
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -451,6 +451,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
> if (++batch_count == SWAP_CLUSTER_MAX) {
> batch_count = 0;
> if (need_resched()) {
> + arch_leave_lazy_mmu_mode();
> pte_unmap_unlock(start_pte, ptl);
> cond_resched();
> goto restart;
On (24/01/25 22:53), Andrew Morton wrote:
> Date: Thu, 25 Jan 2024 22:53:36 -0800
> From: Andrew Morton <[email protected]>
> To: Sergey Senozhatsky <[email protected]>
> Cc: Jiexun Wang <[email protected]>, [email protected],
> [email protected]
> Subject: Re: [PATCH] mm/madvise: don't forget to leave lazy MMU mode in
> madvise_cold_or_pageout_pte_range()
> Message-Id: <[email protected]>
> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu)
>
> On Fri, 26 Jan 2024 12:25:48 +0900 Sergey Senozhatsky <[email protected]> wrote:
>
> > We need to leave lazy MMU mode before unlocking.
It depends on the arch, as far as I understand it.
We can enter lazy MMU mode (on each goto restart) more times than leave
it, and, for isntance, on powerpc that means that we can preempt_disable()
more times than preempt_enable(). That's how enter/leave lazy MMU mode is
implemented there:
static inline void arch_enter_lazy_mmu_mode(void)
{
struct ppc64_tlb_batch *batch;
if (radix_enabled())
return;
/*
* apply_to_page_range can call us this preempt enabled when
* operating on kernel page tables.
*/
preempt_disable();
batch = this_cpu_ptr(&ppc64_tlb_batch);
batch->active = 1;
}
static inline void arch_leave_lazy_mmu_mode(void)
{
struct ppc64_tlb_batch *batch;
if (radix_enabled())
return;
batch = this_cpu_ptr(&ppc64_tlb_batch);
if (batch->index)
__flush_tlb_pending(batch);
batch->active = 0;
preempt_enable();
}
> What might be the userspace-visible effects of this?
>
> > Fixes: b2f557a21bc8 ("mm/madvise: add cond_resched() in madvise_cold_or_pageout_pte_range()"
> > Signed-off-by: Sergey Senozhatsky <[email protected]>
>
> I'll add a cc:stable.
Thanks.