linux-kernel - Re: [RFC PATCH v5] f2fs: support data compression

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Message-ID: <f8072007-94c9-6d37-b0ff-37538cf8bf98@huawei.com>
Date:   Mon, 23 Dec 2019 11:36:51 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     Jaegeuk Kim <jaegeuk@...nel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Chao Yu <chao@...nel.org>
Subject: Re: [RFC PATCH v5] f2fs: support data compression

On 2019/12/19 17:53, Geert Uytterhoeven wrote:
> On Mon, Dec 16, 2019 at 7:29 AM Chao Yu <yuchao0@...wei.com> wrote:
>> This patch tries to support compression in f2fs.
> 
>> +static int f2fs_write_raw_pages(struct compress_ctx *cc,
>> +                                       int *submitted,
>> +                                       struct writeback_control *wbc,
>> +                                       enum iostat_type io_type,
>> +                                       bool compressed)
>> +{
>> +       int i, _submitted;
>> +       int ret, err = 0;
>> +
>> +       for (i = 0; i < cc->cluster_size; i++) {
>> +               if (!cc->rpages[i])
>> +                       continue;
>> +retry_write:
>> +               BUG_ON(!PageLocked(cc->rpages[i]));
>> +
>> +               ret = f2fs_write_single_data_page(cc->rpages[i], &_submitted,
>> +                                               NULL, NULL, wbc, io_type);
>> +               if (ret) {
>> +                       if (ret == AOP_WRITEPAGE_ACTIVATE) {
>> +                               unlock_page(cc->rpages[i]);
>> +                               ret = 0;
>> +                       } else if (ret == -EAGAIN) {
>> +                               ret = 0;
>> +                               cond_resched();
>> +                               congestion_wait(BLK_RW_ASYNC, HZ/50);
> 
> On some platforms, HZ can be less than 50.
> What happens if congestion_wait() is called with a zero timeout?

Thanks for the report, will fix in a separated patch.

Thanks,

> 
>> +                               lock_page(cc->rpages[i]);
>> +                               clear_page_dirty_for_io(cc->rpages[i]);
>> +                               goto retry_write;
>> +                       }
>> +                       err = ret;
>> +                       goto out_fail;
>> +               }
>> +
>> +               *submitted += _submitted;
>> +       }
>> +       return 0;
>> +
>> +out_fail:
>> +       /* TODO: revoke partially updated block addresses */
>> +       BUG_ON(compressed);
>> +
>> +       for (++i; i < cc->cluster_size; i++) {
>> +               if (!cc->rpages[i])
>> +                       continue;
>> +               redirty_page_for_writepage(wbc, cc->rpages[i]);
>> +               unlock_page(cc->rpages[i]);
>> +       }
>> +       return err;
>> +}
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
>