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Sun, 29 Jan 2023 03:18:43 -0800 (PST) Date: Sun, 29 Jan 2023 19:18:37 +0800 From: qixiaoyu To: Chao Yu , Jaegeuk Kim Message-ID: References: <20230113125859.15651-1-qixiaoyu1@xiaomi.com> <20230116030850.20260-1-qixiaoyu1@xiaomi.com> <7c12ebaa-4d3d-e475-dfb2-7b459cd26e64@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <7c12ebaa-4d3d-e475-dfb2-7b459cd26e64@kernel.org> X-Headers-End: 1pM5hx-002QKR-NX Subject: Re: [f2fs-dev] [PATCH 1/2 v2] f2fs: fix wrong calculation of block age X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: xiongping1@xiaomi.com, qixiaoyu1@xiaomi.com, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Sat, Jan 28, 2023 at 11:35:34AM +0800, Chao Yu wrote: > On 2023/1/16 11:08, qixiaoyu1 wrote: > > Currently we wrongly calculate the new block age to > > old * LAST_AGE_WEIGHT / 100. > > > > Fix it to new * (100 - LAST_AGE_WEIGHT) / 100 > > + old * LAST_AGE_WEIGHT / 100. > > > > Signed-off-by: qixiaoyu1 > > Signed-off-by: xiongping1 > > --- > > Change log v1 -> v2: > > - fix udiv > > > > fs/f2fs/extent_cache.c | 7 ++----- > > 1 file changed, 2 insertions(+), 5 deletions(-) > > > > diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c > > index 342af24b2f8c..ad5533f178fd 100644 > > --- a/fs/f2fs/extent_cache.c > > +++ b/fs/f2fs/extent_cache.c > > @@ -874,11 +874,8 @@ void f2fs_update_read_extent_tree_range_compressed(struct inode *inode, > > static unsigned long long __calculate_block_age(unsigned long long new, > > unsigned long long old) > > { > > - unsigned long long diff; > > - > > - diff = (new >= old) ? new - (new - old) : new + (old - new); > > - > > - return div_u64(diff * LAST_AGE_WEIGHT, 100); > > + return div_u64(new, 100) * (100 - LAST_AGE_WEIGHT) > > + + div_u64(old, 100) * LAST_AGE_WEIGHT; > > How about updating as below to avoid lossing accuracy if new is less than 100? > > return div_u64(new * (100 - LAST_AGE_WEIGHT), 100) + > div_u64(old * LAST_AGE_WEIGHT, 100); > > Thanks, > We want to avoid overflow by doing the division first. To keep the accuracy, how about updating as below: res = div_u64_rem(new, 100, &rem_new) * (100 - LAST_AGE_WEIGHT) + div_u64_rem(old, 100, &rem_old) * LAST_AGE_WEIGHT; res += rem_new * (100 - LAST_AGE_WEIGHT) / 100 + rem_old * LAST_AGE_WEIGHT / 100; return res; Thanks, > > } > > /* This returns a new age and allocated blocks in ei */ _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel