linux-kernel - Re: [PATCH v2] f2fs: fix indefinite loop scanning for free nid

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Message-ID: <f0504d96-6972-a6db-ec52-aa59bd354d98@huawei.com>
Date:   Wed, 19 Aug 2020 09:35:52 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Sahitya Tummala <stummala@...eaurora.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] f2fs: fix indefinite loop scanning for free nid

On 2020/8/18 18:10, Sahitya Tummala wrote:
> If the sbi->ckpt->next_free_nid is not NAT block aligned and if there
> are free nids in that NAT block between the start of the block and
> next_free_nid, then those free nids will not be scanned in scan_nat_page().
> This results into mismatch between nm_i->available_nids and the sum of
> nm_i->free_nid_count of all NAT blocks scanned. And nm_i->available_nids
> will always be greater than the sum of free nids in all the blocks.
> Under this condition, if we use all the currently scanned free nids,
> then it will loop forever in f2fs_alloc_nid() as nm_i->available_nids
> is still not zero but nm_i->free_nid_count of that partially scanned
> NAT block is zero.
> 
> Fix this to align the nm_i->next_scan_nid to the first nid of the
> corresponding NAT block.
> 
> Signed-off-by: Sahitya Tummala <stummala@...eaurora.org>

Reviewed-by: Chao Yu <yuchao0@...wei.com>

 > During CP we update only ckpt->next_free_nid but not
 > the nm_i->next_free_nid, which is done only once during boot up.

Oops, thanks for correcting that...

Thanks,