lkml.org 
[lkml]   [2019]   [May]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC 7/7] mm: madvise support MADV_ANONYMOUS_FILTER and MADV_FILE_FILTER
On Mon, May 20, 2019 at 11:28:01AM +0200, Michal Hocko wrote:
> [cc linux-api]
>
> On Mon 20-05-19 12:52:54, Minchan Kim wrote:
> > System could have much faster swap device like zRAM. In that case, swapping
> > is extremely cheaper than file-IO on the low-end storage.
> > In this configuration, userspace could handle different strategy for each
> > kinds of vma. IOW, they want to reclaim anonymous pages by MADV_COLD
> > while it keeps file-backed pages in inactive LRU by MADV_COOL because
> > file IO is more expensive in this case so want to keep them in memory
> > until memory pressure happens.
> >
> > To support such strategy easier, this patch introduces
> > MADV_ANONYMOUS_FILTER and MADV_FILE_FILTER options in madvise(2) like
> > that /proc/<pid>/clear_refs already has supported same filters.
> > They are filters could be Ored with other existing hints using top two bits
> > of (int behavior).
>
> madvise operates on top of ranges and it is quite trivial to do the
> filtering from the userspace so why do we need any additional filtering?
>
> > Once either of them is set, the hint could affect only the interested vma
> > either anonymous or file-backed.
> >
> > With that, user could call a process_madvise syscall simply with a entire
> > range(0x0 - 0xFFFFFFFFFFFFFFFF) but either of MADV_ANONYMOUS_FILTER and
> > MADV_FILE_FILTER so there is no need to call the syscall range by range.
>
> OK, so here is the reason you want that. The immediate question is why
> cannot the monitor do the filtering from the userspace. Slightly more
> work, all right, but less of an API to expose and that itself is a
> strong argument against.

What I should do if we don't have such filter option is to enumerate all of
vma via /proc/<pid>/maps and then parse every ranges and inode from string,
which would be painful for 2000+ vmas.

>
> > * from v1r2
> > * use consistent check with clear_refs to identify anon/file vma - surenb
> >
> > * from v1r1
> > * use naming "filter" for new madvise option - dancol
> >
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> > include/uapi/asm-generic/mman-common.h | 5 +++++
> > mm/madvise.c | 14 ++++++++++++++
> > 2 files changed, 19 insertions(+)
> >
> > diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
> > index b8e230de84a6..be59a1b90284 100644
> > --- a/include/uapi/asm-generic/mman-common.h
> > +++ b/include/uapi/asm-generic/mman-common.h
> > @@ -66,6 +66,11 @@
> > #define MADV_WIPEONFORK 18 /* Zero memory on fork, child only */
> > #define MADV_KEEPONFORK 19 /* Undo MADV_WIPEONFORK */
> >
> > +#define MADV_BEHAVIOR_MASK (~(MADV_ANONYMOUS_FILTER|MADV_FILE_FILTER))
> > +
> > +#define MADV_ANONYMOUS_FILTER (1<<31) /* works for only anonymous vma */
> > +#define MADV_FILE_FILTER (1<<30) /* works for only file-backed vma */
> > +
> > /* compatibility flags */
> > #define MAP_FILE 0
> >
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index f4f569dac2bd..116131243540 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -1002,7 +1002,15 @@ static int madvise_core(struct task_struct *tsk, unsigned long start,
> > int write;
> > size_t len;
> > struct blk_plug plug;
> > + bool anon_only, file_only;
> >
> > + anon_only = behavior & MADV_ANONYMOUS_FILTER;
> > + file_only = behavior & MADV_FILE_FILTER;
> > +
> > + if (anon_only && file_only)
> > + return error;
> > +
> > + behavior = behavior & MADV_BEHAVIOR_MASK;
> > if (!madvise_behavior_valid(behavior))
> > return error;
> >
> > @@ -1067,12 +1075,18 @@ static int madvise_core(struct task_struct *tsk, unsigned long start,
> > if (end < tmp)
> > tmp = end;
> >
> > + if (anon_only && vma->vm_file)
> > + goto next;
> > + if (file_only && !vma->vm_file)
> > + goto next;
> > +
> > /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
> > error = madvise_vma(tsk, vma, &prev, start, tmp,
> > behavior, &pages);
> > if (error)
> > goto out;
> > *nr_pages += pages;
> > +next:
> > start = tmp;
> > if (prev && start < prev->vm_end)
> > start = prev->vm_end;
> > --
> > 2.21.0.1020.gf2820cf01a-goog
> >
>
> --
> Michal Hocko
> SUSE Labs

\
 
 \ /
  Last update: 2019-05-21 04:57    [W:0.205 / U:2.124 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site