On Tue, Oct 20, 2020 at 2:06 AM SeongJae Park <sjpark@xxxxxxxxxx> wrote: > > From: SeongJae Park <sjpark@xxxxxxxxx> > > This commit introduces a reference implementation of the address space > specific low level primitives for the virtual address space, so that > users of DAMON can easily monitor the data accesses on virtual address > spaces of specific processes by simply configuring the implementation to > be used by DAMON. > > The low level primitives for the fundamental access monitoring are > defined in two parts: > 1. Identification of the monitoring target address range for the address > space. > 2. Access check of specific address range in the target space. > > The reference implementation for the virtual address space provided by > this commit is designed as below. > > PTE Accessed-bit Based Access Check > ----------------------------------- > > The implementation uses PTE Accessed-bit for basic access checks. That > is, it clears the bit for next sampling target page and checks whether > it set again after one sampling period. This could disturb other kernel > subsystems using the Accessed bits, namely Idle page tracking and the > reclaim logic. To avoid such disturbances, DAMON makes it mutually > exclusive with Idle page tracking and uses ``PG_idle`` and ``PG_young`` > page flags to solve the conflict with the reclaim logics, as Idle page > tracking does. > > VMA-based Target Address Range Construction > ------------------------------------------- > > Only small parts in the super-huge virtual address space of the > processes are mapped to physical memory and accessed. Thus, tracking > the unmapped address regions is just wasteful. However, because DAMON > can deal with some level of noise using the adaptive regions adjustment > mechanism, tracking every mapping is not strictly required but could > even incur a high overhead in some cases. That said, too huge unmapped > areas inside the monitoring target should be removed to not take the > time for the adaptive mechanism. > > For the reason, this implementation converts the complex mappings to > three distinct regions that cover every mapped area of the address > space. Also, the two gaps between the three regions are the two biggest > unmapped areas in the given address space. The two biggest unmapped > areas would be the gap between the heap and the uppermost mmap()-ed > region, and the gap between the lowermost mmap()-ed region and the stack > in most of the cases. Because these gaps are exceptionally huge in > usual address spacees, excluding these will be sufficient to make a > reasonable trade-off. Below shows this in detail:: > > <heap> > <BIG UNMAPPED REGION 1> > <uppermost mmap()-ed region> > (small mmap()-ed regions and munmap()-ed regions) > <lowermost mmap()-ed region> > <BIG UNMAPPED REGION 2> > <stack> > > Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx> > Reviewed-by: Leonard Foerster <foersleo@xxxxxxxxx> > --- > include/linux/damon.h | 14 + > mm/damon/Kconfig | 10 + > mm/damon/Makefile | 1 + > mm/damon/primitives.c | 582 ++++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 607 insertions(+) > create mode 100644 mm/damon/primitives.c > > diff --git a/include/linux/damon.h b/include/linux/damon.h > index b8562814751e..70cc4b54212e 100644 > --- a/include/linux/damon.h > +++ b/include/linux/damon.h > @@ -238,4 +238,18 @@ int damon_stop(struct damon_ctx **ctxs, int nr_ctxs); > > #endif /* CONFIG_DAMON */ > > +#ifdef CONFIG_DAMON_PRIMITIVES > + > +/* Reference callback implementations for virtual memory */ > +void damon_va_init_regions(struct damon_ctx *ctx); > +void damon_va_update_regions(struct damon_ctx *ctx); > +void damon_va_prepare_access_checks(struct damon_ctx *ctx); > +unsigned int damon_va_check_accesses(struct damon_ctx *ctx); > +bool damon_va_target_valid(struct damon_target *t); > +void damon_va_cleanup(struct damon_ctx *ctx); > +void damon_va_set_primitives(struct damon_ctx *ctx); > + > +#endif /* CONFIG_DAMON_PRIMITIVES */ > + > + > #endif > diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig > index d00e99ac1a15..0d2a18ddb9d8 100644 > --- a/mm/damon/Kconfig > +++ b/mm/damon/Kconfig > @@ -12,4 +12,14 @@ config DAMON > See https://damonitor.github.io/doc/html/latest-damon/index.html for > more information. > > +config DAMON_PRIMITIVES I would rather name this base on virtual address space monitoring maybe like DAMON_VMA_OPTIMIZED_MONITORING or something similar. PRIMITIVES does not seem like a good name for this. > + bool "Monitoring primitives for virtual address spaces monitoring" > + depends on DAMON && MMU && !IDLE_PAGE_TRACKING > + select PAGE_EXTENSION if !64BIT > + select PAGE_IDLE_FLAG > + help > + This builds the default data access monitoring primitives for DAMON. > + The primitives support only virtual address spaces. If this cannot > + cover your use case, you can implement and use your own primitives. > + > endmenu > diff --git a/mm/damon/Makefile b/mm/damon/Makefile > index 4fd2edb4becf..2f3235a52e5e 100644 > --- a/mm/damon/Makefile > +++ b/mm/damon/Makefile > @@ -1,3 +1,4 @@ > # SPDX-License-Identifier: GPL-2.0 > > obj-$(CONFIG_DAMON) := core.o > +obj-$(CONFIG_DAMON_PRIMITIVES) += primitives.o > diff --git a/mm/damon/primitives.c b/mm/damon/primitives.c > new file mode 100644 > index 000000000000..9b603ac0077c > --- /dev/null > +++ b/mm/damon/primitives.c Same with the filename. > @@ -0,0 +1,582 @@ > +// SPDX-License-Identifier: GPL-2.0 [snip] > +static bool damon_va_young(struct mm_struct *mm, unsigned long addr, > + unsigned long *page_sz) > +{ > + pte_t *pte = NULL; > + pmd_t *pmd = NULL; > + spinlock_t *ptl; > + bool young = false; > + > + if (follow_pte_pmd(mm, addr, NULL, &pte, &pmd, &ptl)) > + return false; > + > + *page_sz = PAGE_SIZE; > + if (pte) { > + young = pte_young(*pte); > + if (!young) > + young = !page_is_idle(pte_page(*pte)); > + pte_unmap_unlock(pte, ptl); > + return young; > + } > + > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > + young = pmd_young(*pmd); > + if (!young) > + young = !page_is_idle(pmd_page(*pmd)); > + spin_unlock(ptl); > + *page_sz = ((1UL) << HPAGE_PMD_SHIFT); > +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > + > + return young; Don't you need mmu_notifier_clear_young() here? I am still looking more into this patch
