linux-kernel - Re: [f2fs-dev] [PATCH 2/2] f2fs: add F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS

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Date:   Fri, 27 Nov 2020 09:30:53 +0900
From:   Daeho Jeong <daeho43@...il.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Chao Yu <yuchao0@...wei.com>, Daeho Jeong <daehojeong@...gle.com>,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 2/2] f2fs: add F2FS_IOC_DECOMPRESS_FILE and F2FS_IOC_COMPRESS_FILE

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.

2020년 11월 27일 (금) 오전 8:46, Daeho Jeong <daeho43@...il.com>님이 작성:
>
> 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,
>
> 2020년 11월 27일 (금) 오전 2:49, Eric Biggers <ebiggers@...nel.org>님이 작성:
> >
> > 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 already
> > > check i_size boundary on our own.
> > > What do you think?
> >
> > What about page_cache_async_readahead() or page_cache_sync_readahead()?
> >
> > - Eric