On Thu, May 06, 2021 at 08:15:40PM +0800, changfeng...@vivo.com wrote:
> This patch will not bring significant performance improvements, I
> test this on mobile phone, use androbench, the sequential write test
> case was open file with O_TRUNC, set write size to 4KB, performance
> improved about 2%-3%. If write size set to 32MB, performance improved
> about 0.5%.
Ok, so considering this, my suggestion is that it'd be better to add
your own configuration and raw test results to the commit message to
show the reason why we need this constraint here.
Also, adding some inline comments about this sounds better.
Thanks,
Gao Xiang
>
>
> -----邮件原件-----
> 发件人: Chao Yu <yuch...@huawei.com>
> 发送时间: 2021年5月6日 18:38
> 收件人: Gao Xiang <hsiang...@aol.com>
> 抄送: Gao Xiang <hsiang...@redhat.com>; changfeng...@vivo.com;
> jaeg...@kernel.org; linux-f2fs-devel@lists.sourceforge.net
> 主题: Re: [f2fs-dev] 答复: [PATCH] f2fs: compress: avoid unnecessary check in
> f2fs_prepare_compress_overwrite
>
> Hi Xiang,
>
> On 2021/5/6 17:58, Gao Xiang wrote:
> > Hi Chao,
> >
> > On Thu, May 06, 2021 at 05:15:04PM +0800, Chao Yu wrote:
> >> On 2021/4/26 17:00, Gao Xiang wrote:
> >>> On Mon, Apr 26, 2021 at 04:42:20PM +0800, changfeng...@vivo.com wrote:
> >>>> Thank you for the reminder, I hadn't thought about fallocate before.
> >>>> I have done some tests and the results are as expected.
> >>>> Here is my test method, create a compressed file, and use fallocate
> >>>> with keep size, when write data to expand area,
> >>>> f2fs_prepare_compress_overwrite always return 0, the behavior is same as
> >>>> my patch , apply my patch can avoid those check.
> >>>> Is there anything else I haven't thought of?
> >>>
> >>> Nope, I didn't look into the implementation. Just a wild guess.
> >>>
> >>> (I just wondered if the cluster size is somewhat large (e.g. 64k),
> >>> but with a partial fallocate (e.g. 16k), and does it behave ok?
> >>> or some other corner cases/conditions are needed.)
> >>
> >> Xiang, sorry for late reply.
> >>
> >> Now, f2fs triggers compression only if one cluster is fully written,
> >> e.g. cluster size is 16kb, isize is 8kb, then the first cluster is
> >> non-compressed one, so we don't need to prepare for compressed
> >> cluster overwrite during write_begin(). Also, blocks fallocated
> >> beyond isize should never be compressed, so we don't need to worry
> >> about that.
> >>
> >
> > Yeah, that could make it unnoticable. but my main concern is actually
> > not what the current runtime compression logic is, but what the
> > on-disk compresion format actually is, or there could cause
> > compatibility issue if some later kernel makes full use of this and
> > use old kernels
>
> That's related, if there is layout v2 or we updated runtime compression
> policy later, it needs to reconsider newly introduced logic of this patch, I
> guess we need to add comments here to indicate why we can skip the
> preparation function.
>
> > instead (also considering some corrupted compression indexes, which is
> > not generated by the normal runtime compression logic.)
>
> Yes, that's good concern, but that was not done by
> f2fs_prepare_compress_overwrite(), another sanity check logic needs to be
> designed and implemented in separated patch.
>
> >
> > My own suggestion about this is still verifying compress indexes first
> > rather than relying much on runtime logic constraint. (Except that
> > this patch can show signifiant benefit performance numbers to prove it
> > can improve performance a lot.) Just my own premature thoughts.
>
> Fengnan, could you please give some numbers to show how that check can impact
> performance?
>
> Thanks,
>
> >
> > Thanks,
> > Gao Xiang
> >
> >> Thanks,
> >>
> >>>
> >>> If that is fine, I have no problem about this, yet i_size here is
> >>> generally somewhat risky since after post-EOF behavior changes (e.g.
> >>> supporting FALLOC_FL_ZERO_RANGE with keep size later), it may cause
> >>> some potential regression.
> >>>
> >>>>
> >>>> -----邮件原件-----
> >>>> 发件人: Gao Xiang <hsiang...@redhat.com>
> >>>> 发送时间: 2021年4月26日 11:19
> >>>> 收件人: Fengnan Chang <changfeng...@vivo.com>
> >>>> 抄送: c...@kernel.org; jaeg...@kernel.org;
> >>>> linux-f2fs-devel@lists.sourceforge.net
> >>>> 主题: Re: [f2fs-dev] [PATCH] f2fs: compress: avoid unnecessary check
> >>>> in f2fs_prepare_compress_overwrite
> >>>>
> >>>> On Mon, Apr 26, 2021 at 10:11:53AM +0800, Fengnan Chang wrote:
> >>>>> when write compressed file with O_TRUNC, there will be a lot of
> >>>>> unnecessary check valid blocks in f2fs_prepare_compress_overwrite,
> >>>>> especially when written in page size, remove it.
> >>>>>
> >>>>> Signed-off-by: Fengnan Chang <changfeng...@vivo.com>
> >>>>
> >>>> Even though I didn't look into the whole thing, my reaction here is
> >>>> roughly how to handle fallocate with keep size? Does it work as expected?
> >>>>
> >>>>> ---
> >>>>> fs/f2fs/data.c | 4 ++++
> >>>>> 1 file changed, 4 insertions(+)
> >>>>>
> >>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c index
> >>>>> cf935474ffba..9c3b0849f35e 100644
> >>>>> --- a/fs/f2fs/data.c
> >>>>> +++ b/fs/f2fs/data.c
> >>>>> @@ -3270,6 +3270,7 @@ static int f2fs_write_begin(struct file
> >>>>> *file, struct address_space *mapping,
> >>>>> struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >>>>> struct page *page = NULL;
> >>>>> pgoff_t index = ((unsigned long long) pos) >> PAGE_SHIFT;
> >>>>> + pgoff_t end = (i_size_read(inode) + PAGE_SIZE - 1) >>
> >>>>> +PAGE_SHIFT;
> >>>>> bool need_balance = false, drop_atomic = false;
> >>>>> block_t blkaddr = NULL_ADDR;
> >>>>> int err = 0;
> >>>>> @@ -3306,6 +3307,9 @@ static int f2fs_write_begin(struct file
> >>>>> *file, struct address_space *mapping,
> >>>>>
> >>>>> *fsdata = NULL;
> >>>>>
> >>>>> + if (index >= end)
> >>>>> + goto repeat;
> >>>>> +
> >>>>> ret = f2fs_prepare_compress_overwrite(inode, pagep,
> >>>>> index, fsdata);
> >>>>> if (ret < 0) {
> >>>>> --
> >>>>> 2.29.0
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>>
> >>>
> >>>
> >>>
> >>> _______________________________________________
> >>> Linux-f2fs-devel mailing list
> >>> Linux-f2fs-devel@lists.sourceforge.net
> >>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> >>>
> >>
> >>
> >> _______________________________________________
> >> Linux-f2fs-devel mailing list
> >> Linux-f2fs-devel@lists.sourceforge.net
> >> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> > .
> >
>
>
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