From: Shakeel Butt <shakeelb@google.com>
To: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Minchan Kim <minchan@kernel.org>,
Tian Tao <tiantao6@hisilicon.com>,
Seth Jennings <sjenning@redhat.com>,
Dan Streetman <ddstreet@ieee.org>,
Andrew Morton <akpm@linux-foundation.org>,
Barry Song <song.bao.hua@hisilicon.com>,
Linux-MM <linux-mm@kvack.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [RFC mm/zswap 1/2] mm/zswap: add the flag can_sleep_mapped
Date: Thu, 14 Jan 2021 11:21:19 -0800 [thread overview]
Message-ID: <CALvZod7C1JYXi=uUX8F+o+qBquWxvV19OVQjPdXguHX8D-PEMA@mail.gmail.com> (raw)
In-Reply-To: <CAM4kBBLsJ4bR1z2wFVW1DhPvcj+d63M-rTCndkbfNoR+GXGYHQ@mail.gmail.com>
On Thu, Jan 14, 2021 at 11:05 AM Vitaly Wool <vitaly.wool@konsulko.com> wrote:
>
> On Thu, Jan 14, 2021 at 7:56 PM Minchan Kim <minchan@kernel.org> wrote:
> >
> > On Thu, Jan 14, 2021 at 07:40:50PM +0100, Vitaly Wool wrote:
> > > On Thu, Jan 14, 2021 at 7:29 PM Minchan Kim <minchan@kernel.org> wrote:
> > > >
> > > > On Fri, Dec 25, 2020 at 07:02:50PM +0800, Tian Tao wrote:
> > > > > add a flag to zpool, named is "can_sleep_mapped", and have it set true
> > > > > for zbud/z3fold, set false for zsmalloc. Then zswap could go the current
> > > > > path if the flag is true; and if it's false, copy data from src to a
> > > > > temporary buffer, then unmap the handle, take the mutex, process the
> > > > > buffer instead of src to avoid sleeping function called from atomic
> > > > > context.
> > > > >
> > > > > Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
> > > > > ---
> > > > > include/linux/zpool.h | 3 +++
> > > > > mm/zpool.c | 13 +++++++++++++
> > > > > mm/zswap.c | 50 +++++++++++++++++++++++++++++++++++++++++++++-----
> > > > > 3 files changed, 61 insertions(+), 5 deletions(-)
> > > > >
> > > > > diff --git a/include/linux/zpool.h b/include/linux/zpool.h
> > > > > index 51bf430..e899701 100644
> > > > > --- a/include/linux/zpool.h
> > > > > +++ b/include/linux/zpool.h
> > > > > @@ -73,6 +73,7 @@ u64 zpool_get_total_size(struct zpool *pool);
> > > > > * @malloc: allocate mem from a pool.
> > > > > * @free: free mem from a pool.
> > > > > * @shrink: shrink the pool.
> > > > > + * @sleep_mapped: whether zpool driver can sleep during map.
> > > >
> > > > I don't think it's a good idea. It just breaks zpool abstraction
> > > > in that it exposes internal implementation to user to avoid issue
> > > > zswap recently introduced. It also conflicts zpool_map_handle's
> > > > semantic.
> > > >
> > > > Rather than introducing another break in zpool due to the new
> > > > zswap feature recenlty introduced, zswap could introduce
> > > > CONFIG_ZSWAP_HW_COMPRESSOR. Once it's configured, zsmalloc could
> > > > be disabled. And with disabling CONFIG_ZSWAP_HW_COMPRESSOR, zswap
> > > > doesn't need to make any bounce buffer copy so that no existing
> > > > zsmalloc user will see performance regression.
> > >
> > > I believe it won't help that much -- the new compressor API presumes
> > > that the caller may sleep during compression and that will be an
> > > accident waiting to happen as long as we use it and keep the handle
> > > mapped in zsmalloc case.
> > >
> > > Or maybe I interpreted you wrong and you are suggesting re-introducing
> > > calls to the old API under this #ifdef, is that the case?
> >
> > Yub. zswap could abstract that part under #ifdef to keep old behavior.
>
> We can reconsider this option when zsmalloc implements reclaim
> callback. So far it's obviously too much a mess for a reason so weak.
>
Sorry I don't understand the link between zsmalloc implementing shrink
callback and this patch. This patch is adding an overhead for all
zswap+zsmalloc users irrespective of availability of hardware. If we
want to add support for new hardware, please add without impacting the
current users.
Shakeel
next prev parent reply other threads:[~2021-01-14 19:21 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-25 11:02 [RFC mm/zswap 0/2] Fix the compatibility of zsmalloc and zswap Tian Tao
2020-12-25 11:02 ` [RFC mm/zswap 1/2] mm/zswap: add the flag can_sleep_mapped Tian Tao
2021-01-14 18:28 ` Minchan Kim
2021-01-14 18:40 ` Vitaly Wool
2021-01-14 18:56 ` Minchan Kim
2021-01-14 19:05 ` Vitaly Wool
2021-01-14 19:21 ` Shakeel Butt [this message]
2021-01-14 19:23 ` Minchan Kim
2021-01-14 19:53 ` Vitaly Wool
2021-01-14 21:09 ` Shakeel Butt
2021-01-14 22:41 ` Vitaly Wool
2021-01-19 1:28 ` tiantao (H)
2021-01-14 18:43 ` Shakeel Butt
2021-01-14 18:53 ` Vitaly Wool
2021-01-21 9:17 ` Vitaly Wool
2021-01-21 23:15 ` Song Bao Hua (Barry Song)
2020-12-25 11:02 ` [RFC mm/zswap 2/2] mm: set the sleep_mapped to true for zbud and z3fold Tian Tao
2021-01-14 18:46 ` [RFC mm/zswap 0/2] Fix the compatibility of zsmalloc and zswap Vitaly Wool
2021-01-15 1:17 ` tiantao (H)
2021-01-19 1:31 ` tiantao (H)
2021-01-19 2:39 ` Mike Galbraith
2021-01-18 13:44 ` Sebastian Andrzej Siewior
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