Re: [PATCH RFC] mm/page_idle: simple idle page tracking for virtual memory

[Konstantin Khlebnikov]

On 23.07.2019 16:46, Joel Fernandes wrote:
> On Tue, Jul 23, 2019 at 02:54:26PM +0300, Konstantin Khlebnikov wrote:
> > The page_idle tracking feature currently requires looking up the pagemap
> > for a process followed by interacting with /sys/kernel/mm/page_idle.
> > This is quite cumbersome and can be error-prone too. If between
> > accessing the per-PID pagemap and the global page_idle bitmap, if
> > something changes with the page then the information is not accurate.
> > More over looking up PFN from pagemap in Android devices is not
> > supported by unprivileged process and requires SYS_ADMIN and gives 0 for
> > the PFN.
> >
> > This patch adds simplified interface which works only with mapped pages:
> > Run: "echo 6 > /proc/pid/clear_refs" to mark all mapped pages as idle.
> > Pages that still idle are marked with bit 57 in /proc/pid/pagemap.
> > Total size of idle pages is shown in /proc/pid/smaps (_rollup).
> >
> > Piece of comment is stolen from Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
>
> This will not work well for the problem at hand, the heap profiler
> (heapprofd) only wants to clear the idle flag for the heap memory area which
> is what it is profiling. There is no reason to do it for all mapped pages.
> Using the /proc/pid/page_idle in my patch, it can be done selectively for
> particular memory areas.
>
> I had previously thought of having an interface that accepts an address
> range to set the idle flag, however that is also more complexity.

Profiler could look into particular area in /proc/pid/smaps
or count idle pages via /proc/pid/pagemap.

Selective /proc/pid/clear_refs is not so hard to add.
Somthing like echo "6 561214d03000-561214d29000" > /proc/pid/clear_refs
might be useful for all other operations.

> thanks,
>
>   - Joel
>
>
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> > Link: https://lore.kernel.org/lkml/20190722213205.140845-1-joel@xxxxxxxxxxxxxxxxx/
> > ---
> >   Documentation/admin-guide/mm/pagemap.rst |    3 ++-
> >   Documentation/filesystems/proc.txt       |    3 +++
> >   fs/proc/task_mmu.c                       |   33 ++++++++++++++++++++++++++++--
> >   3 files changed, 36 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
> > index 340a5aee9b80..d7ee60287584 100644
> > --- a/Documentation/admin-guide/mm/pagemap.rst
> > +++ b/Documentation/admin-guide/mm/pagemap.rst
> > @@ -21,7 +21,8 @@ There are four components to pagemap:
> >       * Bit  55    pte is soft-dirty (see
> >         :ref:`Documentation/admin-guide/mm/soft-dirty.rst <soft_dirty>`)
> >       * Bit  56    page exclusively mapped (since 4.2)
> > -    * Bits 57-60 zero
> > +    * Bit  57    page is idle
> > +    * Bits 58-60 zero
> >       * Bit  61    page is file-page or shared-anon (since 3.5)
> >       * Bit  62    page swapped
> >       * Bit  63    page present
> > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> > index 99ca040e3f90..d222be8b4eb9 100644
> > --- a/Documentation/filesystems/proc.txt
> > +++ b/Documentation/filesystems/proc.txt
> > @@ -574,6 +574,9 @@ To reset the peak resident set size ("high water mark") to the process's
> >   current value:
> >       > echo 5 > /proc/PID/clear_refs
> >   
> > +To mark all mapped pages as idle:
> > +    > echo 6 > /proc/PID/clear_refs
> > +
> >   Any other value written to /proc/PID/clear_refs will have no effect.
> >   
> >   The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 731642e0f5a0..6da952574a1f 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -413,6 +413,7 @@ struct mem_size_stats {
> >   	unsigned long private_clean;
> >   	unsigned long private_dirty;
> >   	unsigned long referenced;
> > +	unsigned long idle;
> >   	unsigned long anonymous;
> >   	unsigned long lazyfree;
> >   	unsigned long anonymous_thp;
> > @@ -479,6 +480,10 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
> >   	if (young || page_is_young(page) || PageReferenced(page))
> >   		mss->referenced += size;
> >   
> > +	/* Not accessed and still idle. */
> > +	if (!young && page_is_idle(page))
> > +		mss->idle += size;
> > +
> >   	/*
> >   	 * Then accumulate quantities that may depend on sharing, or that may
> >   	 * differ page-by-page.
> > @@ -799,6 +804,9 @@ static void __show_smap(struct seq_file *m, const struct mem_size_stats *mss,
> >   	SEQ_PUT_DEC(" kB\nPrivate_Clean:  ", mss->private_clean);
> >   	SEQ_PUT_DEC(" kB\nPrivate_Dirty:  ", mss->private_dirty);
> >   	SEQ_PUT_DEC(" kB\nReferenced:     ", mss->referenced);
> > +#ifdef CONFIG_IDLE_PAGE_TRACKING
> > +	SEQ_PUT_DEC(" kB\nIdle:           ", mss->idle);
> > +#endif
> >   	SEQ_PUT_DEC(" kB\nAnonymous:      ", mss->anonymous);
> >   	SEQ_PUT_DEC(" kB\nLazyFree:       ", mss->lazyfree);
> >   	SEQ_PUT_DEC(" kB\nAnonHugePages:  ", mss->anonymous_thp);
> > @@ -969,6 +977,7 @@ enum clear_refs_types {
> >   	CLEAR_REFS_MAPPED,
> >   	CLEAR_REFS_SOFT_DIRTY,
> >   	CLEAR_REFS_MM_HIWATER_RSS,
> > +	CLEAR_REFS_SOFT_ACCESS,
> >   	CLEAR_REFS_LAST,
> >   };
> >   
> > @@ -1045,6 +1054,7 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
> >   	pte_t *pte, ptent;
> >   	spinlock_t *ptl;
> >   	struct page *page;
> > +	int young;
> >   
> >   	ptl = pmd_trans_huge_lock(pmd, vma);
> >   	if (ptl) {
> > @@ -1058,8 +1068,16 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
> >   
> >   		page = pmd_page(*pmd);
> >   
> > +		young = pmdp_test_and_clear_young(vma, addr, pmd);
> > +
> > +		if (cp->type == CLEAR_REFS_SOFT_ACCESS) {
> > +			if (young)
> > +				set_page_young(page);
> > +			set_page_idle(page);
> > +			goto out;
> > +		}
> > +
> >   		/* Clear accessed and referenced bits. */
> > -		pmdp_test_and_clear_young(vma, addr, pmd);
> >   		test_and_clear_page_young(page);
> >   		ClearPageReferenced(page);
> >   out:
> > @@ -1086,8 +1104,16 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
> >   		if (!page)
> >   			continue;
> >   
> > +		young = ptep_test_and_clear_young(vma, addr, pte);
> > +
> > +		if (cp->type == CLEAR_REFS_SOFT_ACCESS) {
> > +			if (young)
> > +				set_page_young(page);
> > +			set_page_idle(page);
> > +			continue;
> > +		}
> > +
> >   		/* Clear accessed and referenced bits. */
> > -		ptep_test_and_clear_young(vma, addr, pte);
> >   		test_and_clear_page_young(page);
> >   		ClearPageReferenced(page);
> >   	}
> > @@ -1253,6 +1279,7 @@ struct pagemapread {
> >   #define PM_PFRAME_MASK		GENMASK_ULL(PM_PFRAME_BITS - 1, 0)
> >   #define PM_SOFT_DIRTY		BIT_ULL(55)
> >   #define PM_MMAP_EXCLUSIVE	BIT_ULL(56)
> > +#define PM_IDLE			BIT_ULL(57)
> >   #define PM_FILE			BIT_ULL(61)
> >   #define PM_SWAP			BIT_ULL(62)
> >   #define PM_PRESENT		BIT_ULL(63)
> > @@ -1326,6 +1353,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
> >   		page = vm_normal_page(vma, addr, pte);
> >   		if (pte_soft_dirty(pte))
> >   			flags |= PM_SOFT_DIRTY;
> > +		if (!pte_young(pte) && page && page_is_idle(page))
> > +			flags |= PM_IDLE;
> >   	} else if (is_swap_pte(pte)) {
> >   		swp_entry_t entry;
> >   		if (pte_swp_soft_dirty(pte))