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SubjectRe: [RFC patch 05/12] LTTng instrumentation mm
* KOSAKI Motohiro (kosaki.motohiro@jp.fujitsu.com) wrote:
> Hi Mathieu,
>
> sorry for late responce.
> I went to business trip few days.
>
>
> > Hi Kosaki,
> >
> > Thanks for this thorough review, please see comments below. Comments
> > without response will be addressed in the next tracepoint release.
>
> thanks.
>
>
> > > > Index: linux-2.6-lttng/mm/memory.c
> > > > ===================================================================
> > > > --- linux-2.6-lttng.orig/mm/memory.c 2008-07-04 18:26:02.000000000 -0400
> > > > +++ linux-2.6-lttng/mm/memory.c 2008-07-04 18:26:37.000000000 -0400
> > > > @@ -51,6 +51,7 @@
> > > > #include <linux/init.h>
> > > > #include <linux/writeback.h>
> > > > #include <linux/memcontrol.h>
> > > > +#include "mm-trace.h"
> > > >
> > > > #include <asm/pgalloc.h>
> > > > #include <asm/uaccess.h>
> > > > @@ -2201,6 +2202,7 @@ static int do_swap_page(struct mm_struct
> > > > /* Had to read the page from swap area: Major fault */
> > > > ret = VM_FAULT_MAJOR;
> > > > count_vm_event(PGMAJFAULT);
> > > > + trace_mm_swap_in(page, entry);
> > > > }
> > > >
> > > > if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
> > >
> > > somebody want get swapin delaying statics.
> > > (see delayacct_set_flag() and delayacct_clear_flag())
> > >
> > > if swap cache exist, swapin can end very faster.
> > > otherwise, spend very long time.
> >
> > I am not sure what you are asking for here ? A supplementary parameter
> > or another trace point ?
>
> Ah, Agreed with my explain is poor.
> my intension was "another trace point".
>

I see. You would like to know the duration of the page fault. Actually,
handle_mm_fault instrumentation gives you both the beginning and end of
page faults. Therefore, instrumenting two locations in swap_in would be
redundant.


>
>
> > > > - if (unlikely(is_vm_hugetlb_page(vma)))
> > > > - return hugetlb_fault(mm, vma, address, write_access);
> > > > + if (unlikely(is_vm_hugetlb_page(vma))) {
> > > > + res = hugetlb_fault(mm, vma, address, write_access);
> > > > + goto end;
> > > > + }
> > > >
> > > > pgd = pgd_offset(mm, address);
> > > > pud = pud_alloc(mm, pgd, address);
> > > > - if (!pud)
> > > > - return VM_FAULT_OOM;
> > > > + if (!pud) {
> > > > + res = VM_FAULT_OOM;
> > > > + goto end;
> > > > + }
> > > > pmd = pmd_alloc(mm, pud, address);
> > > > - if (!pmd)
> > > > - return VM_FAULT_OOM;
> > > > + if (!pmd) {
> > > > + res = VM_FAULT_OOM;
> > > > + goto end;
> > > > + }
> > > > pte = pte_alloc_map(mm, pmd, address);
> > > > - if (!pte)
> > > > - return VM_FAULT_OOM;
> > > > + if (!pte) {
> > > > + res = VM_FAULT_OOM;
> > > > + goto end;
> > > > + }
> > > >
> > > > - return handle_pte_fault(mm, vma, address, pte, pmd, write_access);
> > > > + res = handle_pte_fault(mm, vma, address, pte, pmd, write_access);
> > > > +end:
> > > > + trace_mm_handle_fault_exit();
> > > > + return res;
> > > > }
> > >
> > > no argument?
> > > if two page fault happend in parallel, how do you sort out this two fault?
> > >
> >
> > By using the current thread identifier in the probe. A PF entry on a given
> > thread must be followed by a matching PF exit for that same thread.
> > There may be other events interleaved between the two. Multiple nested
> > page faults shouldn't but *could* happen. In this case, the outermost PF
> > goes with the outermose PF end, and the innermost PF goes with the
> > innermost PF end.
>
> okey.
>
>
> > > and, IMHO res variable is very important.
> > > because it is OOM related.
> > > many MM trouble shooting is worked for OOM related.
> > >
> >
> > Ok, I'll add "res".
>
> Thanks.
>
>
>
> > > > @@ -510,6 +511,8 @@ static void __free_pages_ok(struct page
> > > > int i;
> > > > int reserved = 0;
> > > >
> > > > + trace_mm_page_free(page, order);
> > > > +
> > > > for (i = 0 ; i < (1 << order) ; ++i)
> > > > reserved += free_pages_check(page + i);
> > > > if (reserved)
> > > > @@ -966,6 +969,8 @@ static void free_hot_cold_page(struct pa
> > > > struct per_cpu_pages *pcp;
> > > > unsigned long flags;
> > > >
> > > > + trace_mm_page_free(page, 0);
> > > > +
> > > > if (PageAnon(page))
> > > > page->mapping = NULL;
> > > > if (free_pages_check(page))
> > > > @@ -1630,6 +1635,7 @@ nopage:
> > > > show_mem();
> > > > }
> > > > got_pg:
> > > > + trace_mm_page_alloc(page, order);
> > > > return page;
> > > > }
> > > >
> > >
> > > please pass current task.
> > > I guess somebody need memory allocation tracking.
> > >
> >
> > Hrm.. "current" is available in the probe. Actually, it's available
> > anywhere in the kernel, do we really want to pass it on the stack ?
>
> you are right.
>
>
> > > > static struct bio *get_swap_bio(gfp_t gfp_flags, pgoff_t index,
> > > > @@ -114,6 +115,7 @@ int swap_writepage(struct page *page, st
> > > > rw |= (1 << BIO_RW_SYNC);
> > > > count_vm_event(PSWPOUT);
> > > > set_page_writeback(page);
> > > > + trace_mm_swap_out(page);
> > > > unlock_page(page);
> > > > submit_bio(rw, bio);
> > > > out:
> > >
> > > this tracepoint probe swapout starting, right.
> > > So, Why you don't probe swapout end?
> > >
> >
> > Does submit_bio() block in this case or is it done asynchronously ? It's
> > of no use to trace swap out "end" when in fact there would be no
> > blocking involved.
>
> umm, ok, I should lern LTTng more.
>
>
> > > > @@ -509,6 +511,7 @@ static struct page *alloc_huge_page(stru
> > > > if (!IS_ERR(page)) {
> > > > set_page_refcounted(page);
> > > > set_page_private(page, (unsigned long) mapping);
> > > > + trace_mm_huge_page_alloc(page);
> > > > }
> > > > return page;
> > > > }
> > >
> > > this tracepoint probe to HugePages_Free change, right?
> > > Why you don't probe HugePages_Total and HugePages_Rsvd change?
> >
> > Adding trace_hugetlb_page_reserve(inode, from, to);
> > and
> > trace_hugetlb_page_unreserve(inode, offset, freed);
> >
> > Do you recommend adding another tracing point to monitor the total
> > hugepages pool changes ?
>
> Yes.
> total number of hugepages can increase by sysctl.
>
> So, it must be logged as swap_on/swap_off.
> if it is not logged, freepages of hugepage meaning is ambiguity, IMHO.
>

Ok, so I am adding :


static struct page *alloc_huge_page(struct vm_area_struct *vma,
unsigned long addr)
trace_hugetlb_page_alloc(page);

int hugetlb_reserve_pages(struct inode *inode, long from, long to)
trace_hugetlb_pages_reserve(inode, from, to, ret);

void hugetlb_unreserve_pages(struct inode *inode, long offset, long
freed)
trace_hugetlb_pages_unreserve(inode, offset, freed);

static void update_and_free_page(struct page *page)
trace_hugetlb_page_release(page);

static void free_huge_page(struct page *page)
trace_hugetlb_page_free(page);

static struct page *alloc_fresh_huge_page_node(int nid)
trace_hugetlb_page_grab(page);

static struct page *alloc_buddy_huge_page(struct vm_area_struct *vma,
unsigned long address)
trace_hugetlb_buddy_pgalloc(page);


static struct page *alloc_huge_page(struct vm_area_struct *vma,
unsigned long addr)
trace_hugetlb_page_alloc(page);


It tracks pages taken from the page allocator and from the buddy
allocator, page released, pages reserved/unreserved and page alloc/free
within hugetlb. Does it seem more appropriate ? The only thing it does
not track is "surplus_huge_pages", which seems to be rather internal to
hugetlb. Do you think tracking it would be useful ?

>
>
> > > > @@ -1310,6 +1311,7 @@ asmlinkage long sys_swapoff(const char _
> > > > swap_map = p->swap_map;
> > > > p->swap_map = NULL;
> > > > p->flags = 0;
> > > > + trace_mm_swap_file_close(swap_file);
> > > > spin_unlock(&swap_lock);
> > > > mutex_unlock(&swapon_mutex);
> > > > vfree(swap_map);
> > >
> > > Why you choose this point?
> >
> > The idea is to monitor swap files so we can eventually know, from a
> > trace, which tracefiles were used during the trace and where they were
> > located. I also have a "swap file list" tracepoint which extracts all
> > the tracefile mappings which I plan to submit later. I normally execute
> > it at trace start.
>
> yeah, thank you good explain.
>
>
> > > and why you don't pass pathname? (you pass it in sys_swapon())
> >
> > Since this other tracepoint gives me the mapping between file
> > descriptor and path name, the pathname becomes unnecessary.
>
> it seems you said only LTTng log analyzer is cool.
> but I hope tracepoint mechanism doesn't depent on LTTng.
>

No, the tracepoints are meant to be used by any in-kernel specialized or
module-based generic tracer, which includes ftrace and eventually
blktrace too.

>
> > > IMHO try_to_unuse cause many memory activity and spend many time and
> > > often cause oom-killer.
> > >
> > > I think this point log is needed by somebody.
> >
> > Should it be considered as part of swapoff ?
>
> hmm, okey, you are right.
> that is not swapoff.
>
> > If it is the case, then
> > maybe should we just move the trace_swap_file_close(swap_file); a little
> > be earlier so it is logged before the try_to_unuse() call ?
>
> No.
> eventually, I will add to some VM activety tracepoint.
> but that can separate swapoff tracepoint.
>
> sorry for my confusion.
>

No problem, thanks for the review!

Mathieu

>
>
>
>

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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