lkml.org 
[lkml]   [2020]   [Jun]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: Re: [RFC v2 7/9] mm/damon: Implement callbacks for physical memory monitoring
    Date
    On Thu, 4 Jun 2020 16:58:13 +0200 David Hildenbrand <david@redhat.com> wrote:

    > On 04.06.20 09:26, SeongJae Park wrote:
    > > On Wed, 3 Jun 2020 18:09:21 +0200 David Hildenbrand <david@redhat.com> wrote:
    > >
    > >> On 03.06.20 16:11, SeongJae Park wrote:
    > >>> From: SeongJae Park <sjpark@amazon.de>
    > >>>
    > >>> This commit implements the four callbacks (->init_target_regions,
    > >>> ->update_target_regions, ->prepare_access_check, and ->check_accesses)
    > >>> for the basic access monitoring of the physical memory address space.
    > >>> By setting the callback pointers to point those, users can easily
    > >>> monitor the accesses to the physical memory.
    > >>>
    > >>> Internally, it uses the PTE Accessed bit, as similar to that of the
    > >>> virtual memory support. Also, it supports only page frames that
    > >>> supported by idle page tracking. Acutally, most of the code is stollen
    > >>> from idle page tracking. Users who want to use other access check
    > >>> primitives and monitor the frames that not supported with this
    > >>> implementation could implement their own callbacks on their own.
    > >>>
    > >>> Signed-off-by: SeongJae Park <sjpark@amazon.de>
    > >>> ---
    > >>> include/linux/damon.h | 5 ++
    > >>> mm/damon.c | 184 ++++++++++++++++++++++++++++++++++++++++++
    > >>> 2 files changed, 189 insertions(+)
    > >>>
    > >>> diff --git a/include/linux/damon.h b/include/linux/damon.h
    > >>> index 1a788bfd1b4e..f96503a532ea 100644
    > >>> --- a/include/linux/damon.h
    > >>> +++ b/include/linux/damon.h
    > >>> @@ -216,6 +216,11 @@ void kdamond_update_vm_regions(struct damon_ctx *ctx);
    > >>> void kdamond_prepare_vm_access_checks(struct damon_ctx *ctx);
    > >>> unsigned int kdamond_check_vm_accesses(struct damon_ctx *ctx);
    > >>>
    > >>> +void kdamond_init_phys_regions(struct damon_ctx *ctx);
    > >>> +void kdamond_update_phys_regions(struct damon_ctx *ctx);
    > >>> +void kdamond_prepare_phys_access_checks(struct damon_ctx *ctx);
    > >>> +unsigned int kdamond_check_phys_accesses(struct damon_ctx *ctx);
    > >>> +
    > >>> int damon_set_pids(struct damon_ctx *ctx, int *pids, ssize_t nr_pids);
    > >>> int damon_set_attrs(struct damon_ctx *ctx, unsigned long sample_int,
    > >>> unsigned long aggr_int, unsigned long regions_update_int,
    > >>> diff --git a/mm/damon.c b/mm/damon.c
    > >>> index f5cbc97a3bbc..6a5c6d540580 100644
    > >>> --- a/mm/damon.c
    > >>> +++ b/mm/damon.c
    > >>> @@ -19,7 +19,9 @@
    > >>> #include <linux/mm.h>
    > >>> #include <linux/module.h>
    > >>> #include <linux/page_idle.h>
    > >>> +#include <linux/pagemap.h>
    > >>> #include <linux/random.h>
    > >>> +#include <linux/rmap.h>
    > >>> #include <linux/sched/mm.h>
    > >>> #include <linux/sched/task.h>
    > >>> #include <linux/slab.h>
    > >>> @@ -480,6 +482,11 @@ void kdamond_init_vm_regions(struct damon_ctx *ctx)
    > >>> }
    > >>> }
    > >>>
    > >>> +/* Do nothing. Users should set the initial regions by themselves */
    > >>> +void kdamond_init_phys_regions(struct damon_ctx *ctx)
    > >>> +{
    > >>> +}
    > >>> +
    > >>> static void damon_mkold(struct mm_struct *mm, unsigned long addr)
    > >>> {
    > >>> pte_t *pte = NULL;
    > >>> @@ -611,6 +618,178 @@ unsigned int kdamond_check_vm_accesses(struct damon_ctx *ctx)
    > >>> return max_nr_accesses;
    > >>> }
    > >>>
    > >>> +/* access check functions for physical address based regions */
    > >>> +
    > >>> +/* This code is stollen from page_idle.c */
    > >>> +static struct page *damon_phys_get_page(unsigned long pfn)
    > >>> +{
    > >>> + struct page *page;
    > >>> + pg_data_t *pgdat;
    > >>> +
    > >>> + if (!pfn_valid(pfn))
    > >>> + return NULL;
    > >>> +
    > >>
    > >> Who provides these pfns? Can these be random pfns, supplied unchecked by
    > >> user space? Or are they at least mapped into some user space process?
    > >
    > > Your guess is right, users can give random physical address and that will be
    > > translated into pfn.
    > >
    >
    > Note the difference to idle tracking: "Idle page tracking only considers
    > user memory pages", this is very different to your use case. Note that
    > this is why there is no pfn_to_online_page() check in page idle code.

    My use case is same to that of idle page. I also ignore non-user pages.
    Actually, this function is for filtering of the non-user pages, which is simply
    stollen from the page_idle.

    >
    > >>
    > >> IOW, do we need a pfn_to_online_page() to make sure the memmap even was
    > >> initialized?
    > >
    > > Thank you for pointing out this! I will use it in the next spin. Also, this
    > > code is stollen from page_idle_get_page(). Seems like it should also be
    > > modified to use it. I will send the patch for it, either.
    >
    > pfn_to_online_page() will only succeed for system RAM pages, not
    > dax/pmem (ZONE_DEVICE). dax/pmem needs special care.
    >
    > I can spot that you are taking references to random struct pages. This
    > looks dangerous to me and might mess in complicated ways with page
    > migration/isolation/onlining/offlining etc. I am not sure if we want that.

    AFAIU, page_idle users can also pass random pfns by randomly accessing the
    bitmap file. Am I missing something?


    Thanks,
    SeongJae Park

    >
    > --
    > Thanks,
    >
    > David / dhildenb

    \
     
     \ /
      Last update: 2020-06-04 17:25    [W:6.056 / U:0.056 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site