Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20201123031751.36811-1-daeho43@gmail.com> <20201123031751.36811-2-daeho43@gmail.com>
 <5b3cb83d-5d0f-c1ca-2cff-f28372dec48e@huawei.com> <CACOAw_xs0dizV_xg4-8ssC8wPRq8eXPw3QhHAFf3S-w3hp9jcg@mail.gmail.com>
 <X7/qr/kVxl3AO/PR@sol.localdomain> <CACOAw_xaJ6pfT_EDqCSaL8UnBVkktXK5N_GXuHT+xzu1ufVacg@mail.gmail.com>
In-Reply-To: <CACOAw_xaJ6pfT_EDqCSaL8UnBVkktXK5N_GXuHT+xzu1ufVacg@mail.gmail.com>
From:   Daeho Jeong <daeho43@gmail.com>
Date:   Fri, 27 Nov 2020 09:30:53 +0900
Message-ID: <CACOAw_wyGrkadW5Z6F_GEGT217q4+=68T0cVjnqx-DKx9HYvDw@mail.gmail.com>
Subject: Re: [f2fs-dev] [PATCH 2/2] f2fs: add F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     Chao Yu <yuchao0@huawei.com>, Daeho Jeong <daehojeong@google.com>,
        kernel-team@android.com, linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Re-thinking about this, page_cache_sync_readahead() is not good for
our situation, it might end up with cluster misaligned reads which
trigger internal duplicated cluster reads.

2020=EB=85=84 11=EC=9B=94 27=EC=9D=BC (=EA=B8=88) =EC=98=A4=EC=A0=84 8:46, =
Daeho Jeong <daeho43@gmail.com>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> Chao,
>
> Got it~
>
> Eric,
>
> Actually, I wanted to detour the internal readahead mechanism using
> page_cache_ra_unbounded() to generate cluster size aligned read
> requests.
> But, page_cache_async_readahead() or page_cache_sync_readahead() can
> be also good enough, since those can compensate for the misaligned
> reads reading more pages in advance.
>
> Thanks,
>
> 2020=EB=85=84 11=EC=9B=94 27=EC=9D=BC (=EA=B8=88) =EC=98=A4=EC=A0=84 2:49=
, Eric Biggers <ebiggers@kernel.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
> >
> > On Thu, Nov 26, 2020 at 02:04:41PM +0900, Daeho Jeong wrote:
> > > Eric,
> > >
> > > do_page_cache_ra() is defined in mm/internal.h for internal use
> > > between in mm, so we cannot use this one right now.
> > > So, I think we could use page_cache_ra_unbounded(), because we alread=
y
> > > check i_size boundary on our own.
> > > What do you think?
> >
> > What about page_cache_async_readahead() or page_cache_sync_readahead()?
> >
> > - Eric