Re: [PATCH v8 08/13] exfat: add exfat cache

["Pali Rohár" <pali.rohar@gmail.com>]

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Hello! This patch looks like a copy-pase of fat cache implementation.
It is possible to avoid duplicating code?

On Friday 20 December 2019 01:24:14 Namjae Jeon wrote:
> This adds the implementation of exfat cache.
> 
> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com>
> ---
>  fs/exfat/cache.c | 325 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 325 insertions(+)
>  create mode 100644 fs/exfat/cache.c
> 
> diff --git a/fs/exfat/cache.c b/fs/exfat/cache.c
> new file mode 100644
> index 000000000000..03d0824fc368
> --- /dev/null
> +++ b/fs/exfat/cache.c
> @@ -0,0 +1,325 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + *  linux/fs/fat/cache.c
> + *
> + *  Written 1992,1993 by Werner Almesberger
> + *
> + *  Mar 1999. AV. Changed cache, so that it uses the starting cluster instead
> + *	of inode number.
> + *  May 1999. AV. Fixed the bogosity with FAT32 (read "FAT28"). Fscking lusers.
> + *  Copyright (C) 2012-2013 Samsung Electronics Co., Ltd.
> + */
> +
> +#include <linux/slab.h>
> +#include <asm/unaligned.h>
> +#include <linux/buffer_head.h>
> +
> +#include "exfat_raw.h"
> +#include "exfat_fs.h"
> +
> +#define EXFAT_CACHE_VALID	0
> +#define EXFAT_MAX_CACHE		16
> +
> +struct exfat_cache {
> +	struct list_head cache_list;
> +	unsigned int nr_contig;	/* number of contiguous clusters */
> +	unsigned int fcluster;	/* cluster number in the file. */
> +	unsigned int dcluster;	/* cluster number on disk. */
> +};
> +
> +struct exfat_cache_id {
> +	unsigned int id;
> +	unsigned int nr_contig;
> +	unsigned int fcluster;
> +	unsigned int dcluster;
> +};
> +
> +static struct kmem_cache *exfat_cachep;
> +
> +static void exfat_cache_init_once(void *c)
> +{
> +	struct exfat_cache *cache = (struct exfat_cache *)c;
> +
> +	INIT_LIST_HEAD(&cache->cache_list);
> +}
> +
> +int exfat_cache_init(void)
> +{
> +	exfat_cachep = kmem_cache_create("exfat_cache",
> +				sizeof(struct exfat_cache),
> +				0, SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD,
> +				exfat_cache_init_once);
> +	if (!exfat_cachep)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
> +void exfat_cache_shutdown(void)
> +{
> +	if (!exfat_cachep)
> +		return;
> +	kmem_cache_destroy(exfat_cachep);
> +}
> +
> +void exfat_cache_init_inode(struct inode *inode)
> +{
> +	struct exfat_inode_info *ei = EXFAT_I(inode);
> +
> +	spin_lock_init(&ei->cache_lru_lock);
> +	ei->nr_caches = 0;
> +	ei->cache_valid_id = EXFAT_CACHE_VALID + 1;
> +	INIT_LIST_HEAD(&ei->cache_lru);
> +}
> +
> +static inline struct exfat_cache *exfat_cache_alloc(void)
> +{
> +	return kmem_cache_alloc(exfat_cachep, GFP_NOFS);
> +}
> +
> +static inline void exfat_cache_free(struct exfat_cache *cache)
> +{
> +	WARN_ON(!list_empty(&cache->cache_list));
> +	kmem_cache_free(exfat_cachep, cache);
> +}
> +
> +static inline void exfat_cache_update_lru(struct inode *inode,
> +		struct exfat_cache *cache)
> +{
> +	struct exfat_inode_info *ei = EXFAT_I(inode);
> +
> +	if (ei->cache_lru.next != &cache->cache_list)
> +		list_move(&cache->cache_list, &ei->cache_lru);
> +}
> +
> +static unsigned int exfat_cache_lookup(struct inode *inode,
> +		unsigned int fclus, struct exfat_cache_id *cid,
> +		unsigned int *cached_fclus, unsigned int *cached_dclus)
> +{
> +	struct exfat_inode_info *ei = EXFAT_I(inode);
> +	static struct exfat_cache nohit = { .fcluster = 0, };
> +	struct exfat_cache *hit = &nohit, *p;
> +	unsigned int offset = EXFAT_EOF_CLUSTER;
> +
> +	spin_lock(&ei->cache_lru_lock);
> +	list_for_each_entry(p, &ei->cache_lru, cache_list) {
> +		/* Find the cache of "fclus" or nearest cache. */
> +		if (p->fcluster <= fclus && hit->fcluster < p->fcluster) {
> +			hit = p;
> +			if (hit->fcluster + hit->nr_contig < fclus) {
> +				offset = hit->nr_contig;
> +			} else {
> +				offset = fclus - hit->fcluster;
> +				break;
> +			}
> +		}
> +	}
> +	if (hit != &nohit) {
> +		exfat_cache_update_lru(inode, hit);
> +
> +		cid->id = ei->cache_valid_id;
> +		cid->nr_contig = hit->nr_contig;
> +		cid->fcluster = hit->fcluster;
> +		cid->dcluster = hit->dcluster;
> +		*cached_fclus = cid->fcluster + offset;
> +		*cached_dclus = cid->dcluster + offset;
> +	}
> +	spin_unlock(&ei->cache_lru_lock);
> +
> +	return offset;
> +}
> +
> +static struct exfat_cache *exfat_cache_merge(struct inode *inode,
> +		struct exfat_cache_id *new)
> +{
> +	struct exfat_inode_info *ei = EXFAT_I(inode);
> +	struct exfat_cache *p;
> +
> +	list_for_each_entry(p, &ei->cache_lru, cache_list) {
> +		/* Find the same part as "new" in cluster-chain. */
> +		if (p->fcluster == new->fcluster) {
> +			if (new->nr_contig > p->nr_contig)
> +				p->nr_contig = new->nr_contig;
> +			return p;
> +		}
> +	}
> +	return NULL;
> +}
> +
> +static void exfat_cache_add(struct inode *inode,
> +		struct exfat_cache_id *new)
> +{
> +	struct exfat_inode_info *ei = EXFAT_I(inode);
> +	struct exfat_cache *cache, *tmp;
> +
> +	if (new->fcluster == EXFAT_EOF_CLUSTER) /* dummy cache */
> +		return;
> +
> +	spin_lock(&ei->cache_lru_lock);
> +	if (new->id != EXFAT_CACHE_VALID &&
> +	    new->id != ei->cache_valid_id)
> +		goto unlock;	/* this cache was invalidated */
> +
> +	cache = exfat_cache_merge(inode, new);
> +	if (cache == NULL) {
> +		if (ei->nr_caches < EXFAT_MAX_CACHE) {
> +			ei->nr_caches++;
> +			spin_unlock(&ei->cache_lru_lock);
> +
> +			tmp = exfat_cache_alloc();
> +			if (!tmp) {
> +				spin_lock(&ei->cache_lru_lock);
> +				ei->nr_caches--;
> +				spin_unlock(&ei->cache_lru_lock);
> +				return;
> +			}
> +
> +			spin_lock(&ei->cache_lru_lock);
> +			cache = exfat_cache_merge(inode, new);
> +			if (cache != NULL) {
> +				ei->nr_caches--;
> +				exfat_cache_free(tmp);
> +				goto out_update_lru;
> +			}
> +			cache = tmp;
> +		} else {
> +			struct list_head *p = ei->cache_lru.prev;
> +
> +			cache = list_entry(p,
> +					struct exfat_cache, cache_list);
> +		}
> +		cache->fcluster = new->fcluster;
> +		cache->dcluster = new->dcluster;
> +		cache->nr_contig = new->nr_contig;
> +	}
> +out_update_lru:
> +	exfat_cache_update_lru(inode, cache);
> +unlock:
> +	spin_unlock(&ei->cache_lru_lock);
> +}
> +
> +/*
> + * Cache invalidation occurs rarely, thus the LRU chain is not updated. It
> + * fixes itself after a while.
> + */
> +static void __exfat_cache_inval_inode(struct inode *inode)
> +{
> +	struct exfat_inode_info *ei = EXFAT_I(inode);
> +	struct exfat_cache *cache;
> +
> +	while (!list_empty(&ei->cache_lru)) {
> +		cache = list_entry(ei->cache_lru.next,
> +				   struct exfat_cache, cache_list);
> +		list_del_init(&cache->cache_list);
> +		ei->nr_caches--;
> +		exfat_cache_free(cache);
> +	}
> +	/* Update. The copy of caches before this id is discarded. */
> +	ei->cache_valid_id++;
> +	if (ei->cache_valid_id == EXFAT_CACHE_VALID)
> +		ei->cache_valid_id++;
> +}
> +
> +void exfat_cache_inval_inode(struct inode *inode)
> +{
> +	struct exfat_inode_info *ei = EXFAT_I(inode);
> +
> +	spin_lock(&ei->cache_lru_lock);
> +	__exfat_cache_inval_inode(inode);
> +	spin_unlock(&ei->cache_lru_lock);
> +}
> +
> +static inline int cache_contiguous(struct exfat_cache_id *cid,
> +		unsigned int dclus)
> +{
> +	cid->nr_contig++;
> +	return cid->dcluster + cid->nr_contig == dclus;
> +}
> +
> +static inline void cache_init(struct exfat_cache_id *cid,
> +		unsigned int fclus, unsigned int dclus)
> +{
> +	cid->id = EXFAT_CACHE_VALID;
> +	cid->fcluster = fclus;
> +	cid->dcluster = dclus;
> +	cid->nr_contig = 0;
> +}
> +
> +int exfat_get_cluster(struct inode *inode, unsigned int cluster,
> +		unsigned int *fclus, unsigned int *dclus,
> +		unsigned int *last_dclus, int allow_eof)
> +{
> +	struct super_block *sb = inode->i_sb;
> +	struct exfat_sb_info *sbi = EXFAT_SB(sb);
> +	unsigned int limit = sbi->num_clusters;
> +	struct exfat_inode_info *ei = EXFAT_I(inode);
> +	struct exfat_cache_id cid;
> +	unsigned int content;
> +
> +	if (ei->start_clu == EXFAT_FREE_CLUSTER) {
> +		exfat_fs_error(sb,
> +			"invalid access to exfat cache (entry 0x%08x)",
> +			ei->start_clu);
> +		return -EIO;
> +	}
> +
> +	*fclus = 0;
> +	*dclus = ei->start_clu;
> +	*last_dclus = *dclus;
> +
> +	/*
> +	 * Don`t use exfat_cache if zero offset or non-cluster allocation
> +	 */
> +	if (cluster == 0 || *dclus == EXFAT_EOF_CLUSTER)
> +		return 0;
> +
> +	cache_init(&cid, EXFAT_EOF_CLUSTER, EXFAT_EOF_CLUSTER);
> +
> +	if (exfat_cache_lookup(inode, cluster, &cid, fclus, dclus) ==
> +			EXFAT_EOF_CLUSTER) {
> +		/*
> +		 * dummy, always not contiguous
> +		 * This is reinitialized by cache_init(), later.
> +		 */
> +		WARN_ON(cid.id != EXFAT_CACHE_VALID ||
> +			cid.fcluster != EXFAT_EOF_CLUSTER ||
> +			cid.dcluster != EXFAT_EOF_CLUSTER ||
> +			cid.nr_contig != 0);
> +	}
> +
> +	if (*fclus == cluster)
> +		return 0;
> +
> +	while (*fclus < cluster) {
> +		/* prevent the infinite loop of cluster chain */
> +		if (*fclus > limit) {
> +			exfat_fs_error(sb,
> +				"detected the cluster chain loop (i_pos %u)",
> +				(*fclus));
> +			return -EIO;
> +		}
> +
> +		if (exfat_ent_get(sb, *dclus, &content))
> +			return -EIO;
> +
> +		*last_dclus = *dclus;
> +		*dclus = content;
> +		(*fclus)++;
> +
> +		if (content == EXFAT_EOF_CLUSTER) {
> +			if (!allow_eof) {
> +				exfat_fs_error(sb,
> +				       "invalid cluster chain (i_pos %u, last_clus 0x%08x is EOF)",
> +				       *fclus, (*last_dclus));
> +				return -EIO;
> +			}
> +
> +			break;
> +		}
> +
> +		if (!cache_contiguous(&cid, *dclus))
> +			cache_init(&cid, *fclus, *dclus);
> +	}
> +
> +	exfat_cache_add(inode, &cid);
> +	return 0;
> +}

-- 
Pali Rohár
pali.rohar@gmail.com

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