linux-kernel - Re: [PATCH v1 9/9] exfat: support multi-cluster for exfat_get

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Message-ID:
 <PUZPR04MB631627BD83F409B370337E4D81B9A@PUZPR04MB6316.apcprd04.prod.outlook.com>
Date: Sun, 4 Jan 2026 07:56:22 +0000
From: "Yuezhang.Mo@...y.com" <Yuezhang.Mo@...y.com>
To: Chi Zhiling <chizhiling@....com>
CC: "brauner@...nel.org" <brauner@...nel.org>,
        "chizhiling@...inos.cn"
	<chizhiling@...inos.cn>,
        "jack@...e.cz" <jack@...e.cz>,
        "linkinjeon@...nel.org" <linkinjeon@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sj1557.seo@...sung.com" <sj1557.seo@...sung.com>,
        "viro@...iv.linux.org.uk"
	<viro@...iv.linux.org.uk>,
        "willy@...radead.org" <willy@...radead.org>
Subject: Re: [PATCH v1 9/9] exfat: support multi-cluster for exfat_get_cluster

> On 12/30/25 17:06, Yuezhang.Mo@...y.com wrote:
>>> +     /*
>>> +      * Return on cache hit to keep the code simple.
>>> +      */
>>> +     if (fclus == cluster) {
>>> +             *count = cid.fcluster + cid.nr_contig - fclus + 1;
>>>                return 0;
>>
>> If 'cid.fcluster + cid.nr_contig - fclus + 1 < *count', how about continuing to collect clusters?
>> The following clusters may be continuous.
>
> I'm glad you noticed this detail. It is necessary to explain this and
> update it in the code comments.
> 
> The main reason why I didn't continue the collection was that the
> subsequent clusters might also exist in the cache. This requires us to
> search the cache again to confirm this, and this action might introduce
> additional performance overhead.
> 
> I think we can continue to collect, but we need to check the cache
> before doing so.
>

So we also need to check the cache in the following, right?

```
        /*
         * Collect the remaining clusters of this contiguous extent.
         */
        if (*dclus != EXFAT_EOF_CLUSTER) {
                unsigned int clu = *dclus;

                /*
                 * Now the cid cache contains the first cluster requested,
                 * Advance the fclus to the last cluster of contiguous
                 * extent, then update the count and cid cache accordingly.
                 */
                while (fclus < end) {
                        if (exfat_ent_get(sb, clu, &content, &bh))
                                goto err;
                        if (++clu != content) {
                                /* TODO: read ahead if content valid */
                                break;
                        }
                        fclus++;
                }
                cid.nr_contig = fclus - cid.fcluster;
                *count = fclus - cluster + 1;
```

>>>
>>> +             while (fclus < end) {
>>> +                     if (exfat_ent_get(sb, clu, &content, &bh))
>>> +                             goto err;
>>> +                     if (++clu != content) {
>>> +                             /* TODO: read ahead if content valid */
>>> +                             break;
>>
>> The next cluster index has been read and will definitely be used.
>> How about add it to the cache?
>
> Good idea!
> will add it in v2,