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

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Date:   Thu, 19 Dec 2019 10:53:52 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Chao Yu <yuchao0@...wei.com>
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 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?

> +                               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

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds