erofs: rename per-CPU buffers to global buffer pool and make it configurable

It will cost more time if compressed buffers are allocated on demand for
low-latency algorithms (like lz4) so EROFS uses per-CPU buffers to keep
compressed data if in-place decompression is unfulfilled.  While it is kind
of wasteful of memory for a device with hundreds of CPUs, and only a small
number of CPUs concurrently decompress most of the time.

This patch renames it as 'global buffer pool' and makes it configurable.
This allows two or more CPUs to share a common buffer to reduce memory
occupation.

Suggested-by: Gao Xiang <xiang@kernel.org>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
Link: https://lore.kernel.org/r/20240402100036.2673604-1-guochunhai@vivo.com
Signed-off-by: Sandeep Dhavale <dhavale@google.com>
Link: https://lore.kernel.org/r/20240408215231.3376659-1-dhavale@google.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/Makefile

@@ -3,7 +3,7 @@
 obj-$(CONFIG_EROFS_FS) += erofs.o
 erofs-objs := super.o inode.o data.o namei.o dir.o sysfs.o
 erofs-$(CONFIG_EROFS_FS_XATTR) += xattr.o
-erofs-$(CONFIG_EROFS_FS_ZIP) += decompressor.o zmap.o zdata.o pcpubuf.o zutil.o
+erofs-$(CONFIG_EROFS_FS_ZIP) += decompressor.o zmap.o zdata.o zutil.o
 erofs-$(CONFIG_EROFS_FS_ZIP_LZMA) += decompressor_lzma.o
 erofs-$(CONFIG_EROFS_FS_ZIP_DEFLATE) += decompressor_deflate.o
 erofs-$(CONFIG_EROFS_FS_ONDEMAND) += fscache.o

fs/erofs/decompressor.c

@@ -54,7 +54,7 @@ static int z_erofs_load_lz4_config(struct super_block *sb,
 	sbi->lz4.max_distance_pages = distance ?
 					DIV_ROUND_UP(distance, PAGE_SIZE) + 1 :
 					LZ4_MAX_DISTANCE_PAGES;
-	return erofs_pcpubuf_growsize(sbi->lz4.max_pclusterblks);
+	return z_erofs_gbuf_growsize(sbi->lz4.max_pclusterblks);
 }
 
 /*
@@ -159,7 +159,7 @@ static void *z_erofs_lz4_handle_overlap(struct z_erofs_lz4_decompress_ctx *ctx,
 docopy:
 	/* Or copy compressed data which can be overlapped to per-CPU buffer */
 	in = rq->in;
-	src = erofs_get_pcpubuf(ctx->inpages);
+	src = z_erofs_get_gbuf(ctx->inpages);
 	if (!src) {
 		DBG_BUGON(1);
 		kunmap_local(inpage);
@@ -260,7 +260,7 @@ static int z_erofs_lz4_decompress_mem(struct z_erofs_lz4_decompress_ctx *ctx,
 	} else if (maptype == 1) {
 		vm_unmap_ram(src, ctx->inpages);
 	} else if (maptype == 2) {
-		erofs_put_pcpubuf(src);
+		z_erofs_put_gbuf(src);
 	} else if (maptype != 3) {
 		DBG_BUGON(1);
 		return -EFAULT;

fs/erofs/internal.h

@@ -463,11 +463,11 @@ int erofs_try_to_free_all_cached_folios(struct erofs_sb_info *sbi,
 					struct erofs_workgroup *egrp);
 int z_erofs_map_blocks_iter(struct inode *inode, struct erofs_map_blocks *map,
 			    int flags);
-void *erofs_get_pcpubuf(unsigned int requiredpages);
+void *z_erofs_get_gbuf(unsigned int requiredpages);
-void erofs_put_pcpubuf(void *ptr);
+void z_erofs_put_gbuf(void *ptr);
-int erofs_pcpubuf_growsize(unsigned int nrpages);
+int z_erofs_gbuf_growsize(unsigned int nrpages);
-void __init erofs_pcpubuf_init(void);
+int __init z_erofs_gbuf_init(void);
-void erofs_pcpubuf_exit(void);
+void z_erofs_gbuf_exit(void);
 int erofs_init_managed_cache(struct super_block *sb);
 int z_erofs_parse_cfgs(struct super_block *sb, struct erofs_super_block *dsb);
 #else
@@ -477,8 +477,8 @@ static inline int erofs_init_shrinker(void) { return 0; }
 static inline void erofs_exit_shrinker(void) {}
 static inline int z_erofs_init_zip_subsystem(void) { return 0; }
 static inline void z_erofs_exit_zip_subsystem(void) {}
-static inline void erofs_pcpubuf_init(void) {}
+static inline int z_erofs_gbuf_init(void) { return 0; }
-static inline void erofs_pcpubuf_exit(void) {}
+static inline void z_erofs_gbuf_exit(void) {}
 static inline int erofs_init_managed_cache(struct super_block *sb) { return 0; }
 #endif	/* !CONFIG_EROFS_FS_ZIP */
 

fs/erofs/pcpubuf.c

@@ -1,148 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-only
-/*
- * Copyright (C) Gao Xiang <xiang@kernel.org>
- *
- * For low-latency decompression algorithms (e.g. lz4), reserve consecutive
- * per-CPU virtual memory (in pages) in advance to store such inplace I/O
- * data if inplace decompression is failed (due to unmet inplace margin for
- * example).
- */
-#include "internal.h"
-
-struct erofs_pcpubuf {
-	raw_spinlock_t lock;
-	void *ptr;
-	struct page **pages;
-	unsigned int nrpages;
-};
-
-static DEFINE_PER_CPU(struct erofs_pcpubuf, erofs_pcb);
-
-void *erofs_get_pcpubuf(unsigned int requiredpages)
-	__acquires(pcb->lock)
-{
-	struct erofs_pcpubuf *pcb = &get_cpu_var(erofs_pcb);
-
-	raw_spin_lock(&pcb->lock);
-	/* check if the per-CPU buffer is too small */
-	if (requiredpages > pcb->nrpages) {
-		raw_spin_unlock(&pcb->lock);
-		put_cpu_var(erofs_pcb);
-		/* (for sparse checker) pretend pcb->lock is still taken */
-		__acquire(pcb->lock);
-		return NULL;
-	}
-	return pcb->ptr;
-}
-
-void erofs_put_pcpubuf(void *ptr) __releases(pcb->lock)
-{
-	struct erofs_pcpubuf *pcb = &per_cpu(erofs_pcb, smp_processor_id());
-
-	DBG_BUGON(pcb->ptr != ptr);
-	raw_spin_unlock(&pcb->lock);
-	put_cpu_var(erofs_pcb);
-}
-
-/* the next step: support per-CPU page buffers hotplug */
-int erofs_pcpubuf_growsize(unsigned int nrpages)
-{
-	static DEFINE_MUTEX(pcb_resize_mutex);
-	static unsigned int pcb_nrpages;
-	struct page *pagepool = NULL;
-	int delta, cpu, ret, i;
-
-	mutex_lock(&pcb_resize_mutex);
-	delta = nrpages - pcb_nrpages;
-	ret = 0;
-	/* avoid shrinking pcpubuf, since no idea how many fses rely on */
-	if (delta <= 0)
-		goto out;
-
-	for_each_possible_cpu(cpu) {
-		struct erofs_pcpubuf *pcb = &per_cpu(erofs_pcb, cpu);
-		struct page **pages, **oldpages;
-		void *ptr, *old_ptr;
-
-		pages = kmalloc_array(nrpages, sizeof(*pages), GFP_KERNEL);
-		if (!pages) {
-			ret = -ENOMEM;
-			break;
-		}
-
-		for (i = 0; i < nrpages; ++i) {
-			pages[i] = erofs_allocpage(&pagepool, GFP_KERNEL);
-			if (!pages[i]) {
-				ret = -ENOMEM;
-				oldpages = pages;
-				goto free_pagearray;
-			}
-		}
-		ptr = vmap(pages, nrpages, VM_MAP, PAGE_KERNEL);
-		if (!ptr) {
-			ret = -ENOMEM;
-			oldpages = pages;
-			goto free_pagearray;
-		}
-		raw_spin_lock(&pcb->lock);
-		old_ptr = pcb->ptr;
-		pcb->ptr = ptr;
-		oldpages = pcb->pages;
-		pcb->pages = pages;
-		i = pcb->nrpages;
-		pcb->nrpages = nrpages;
-		raw_spin_unlock(&pcb->lock);
-
-		if (!oldpages) {
-			DBG_BUGON(old_ptr);
-			continue;
-		}
-
-		if (old_ptr)
-			vunmap(old_ptr);
-free_pagearray:
-		while (i)
-			erofs_pagepool_add(&pagepool, oldpages[--i]);
-		kfree(oldpages);
-		if (ret)
-			break;
-	}
-	pcb_nrpages = nrpages;
-	erofs_release_pages(&pagepool);
-out:
-	mutex_unlock(&pcb_resize_mutex);
-	return ret;
-}
-
-void __init erofs_pcpubuf_init(void)
-{
-	int cpu;
-
-	for_each_possible_cpu(cpu) {
-		struct erofs_pcpubuf *pcb = &per_cpu(erofs_pcb, cpu);
-
-		raw_spin_lock_init(&pcb->lock);
-	}
-}
-
-void erofs_pcpubuf_exit(void)
-{
-	int cpu, i;
-
-	for_each_possible_cpu(cpu) {
-		struct erofs_pcpubuf *pcb = &per_cpu(erofs_pcb, cpu);
-
-		if (pcb->ptr) {
-			vunmap(pcb->ptr);
-			pcb->ptr = NULL;
-		}
-		if (!pcb->pages)
-			continue;
-
-		for (i = 0; i < pcb->nrpages; ++i)
-			if (pcb->pages[i])
-				put_page(pcb->pages[i]);
-		kfree(pcb->pages);
-		pcb->pages = NULL;
-	}
-}

fs/erofs/super.c

@@ -859,7 +859,10 @@ static int __init erofs_module_init(void)
 	if (err)
 		goto deflate_err;
 
-	erofs_pcpubuf_init();
+	err = z_erofs_gbuf_init();
+	if (err)
+		goto gbuf_err;
+
 	err = z_erofs_init_zip_subsystem();
 	if (err)
 		goto zip_err;
@@ -879,6 +882,8 @@ fs_err:
 sysfs_err:
 	z_erofs_exit_zip_subsystem();
 zip_err:
+	z_erofs_gbuf_exit();
+gbuf_err:
 	z_erofs_deflate_exit();
 deflate_err:
 	z_erofs_lzma_exit();
@@ -902,7 +907,7 @@ static void __exit erofs_module_exit(void)
 	z_erofs_lzma_exit();
 	erofs_exit_shrinker();
 	kmem_cache_destroy(erofs_inode_cachep);
-	erofs_pcpubuf_exit();
+	z_erofs_gbuf_exit();
 }
 
 static int erofs_statfs(struct dentry *dentry, struct kstatfs *buf)

fs/erofs/zutil.c

@@ -5,6 +5,18 @@
  */
 #include "internal.h"
 
+struct z_erofs_gbuf {
+	spinlock_t lock;
+	void *ptr;
+	struct page **pages;
+	unsigned int nrpages;
+};
+
+static struct z_erofs_gbuf *z_erofs_gbufpool;
+static unsigned int z_erofs_gbuf_count, z_erofs_gbuf_nrpages;
+
+module_param_named(global_buffers, z_erofs_gbuf_count, uint, 0444);
+
 static atomic_long_t erofs_global_shrink_cnt;	/* for all mounted instances */
 /* protected by 'erofs_sb_list_lock' */
 static unsigned int shrinker_run_no;
@@ -14,6 +26,142 @@ static DEFINE_SPINLOCK(erofs_sb_list_lock);
 static LIST_HEAD(erofs_sb_list);
 static struct shrinker *erofs_shrinker_info;
 
+static unsigned int z_erofs_gbuf_id(void)
+{
+	return raw_smp_processor_id() % z_erofs_gbuf_count;
+}
+
+void *z_erofs_get_gbuf(unsigned int requiredpages)
+	__acquires(gbuf->lock)
+{
+	struct z_erofs_gbuf *gbuf;
+
+	gbuf = &z_erofs_gbufpool[z_erofs_gbuf_id()];
+	spin_lock(&gbuf->lock);
+	/* check if the buffer is too small */
+	if (requiredpages > gbuf->nrpages) {
+		spin_unlock(&gbuf->lock);
+		/* (for sparse checker) pretend gbuf->lock is still taken */
+		__acquire(gbuf->lock);
+		return NULL;
+	}
+	return gbuf->ptr;
+}
+
+void z_erofs_put_gbuf(void *ptr) __releases(gbuf->lock)
+{
+	struct z_erofs_gbuf *gbuf;
+
+	gbuf = &z_erofs_gbufpool[z_erofs_gbuf_id()];
+	DBG_BUGON(gbuf->ptr != ptr);
+	spin_unlock(&gbuf->lock);
+}
+
+int z_erofs_gbuf_growsize(unsigned int nrpages)
+{
+	static DEFINE_MUTEX(gbuf_resize_mutex);
+	struct page *pagepool = NULL;
+	int delta, ret, i, j;
+
+	mutex_lock(&gbuf_resize_mutex);
+	delta = nrpages - z_erofs_gbuf_nrpages;
+	ret = 0;
+	/* avoid shrinking gbufs, since no idea how many fses rely on */
+	if (delta <= 0)
+		goto out;
+
+	for (i = 0; i < z_erofs_gbuf_count; ++i) {
+		struct z_erofs_gbuf *gbuf = &z_erofs_gbufpool[i];
+		struct page **pages, **tmp_pages;
+		void *ptr, *old_ptr = NULL;
+
+		ret = -ENOMEM;
+		tmp_pages = kcalloc(nrpages, sizeof(*tmp_pages), GFP_KERNEL);
+		if (!tmp_pages)
+			break;
+		for (j = 0; j < nrpages; ++j) {
+			tmp_pages[j] = erofs_allocpage(&pagepool, GFP_KERNEL);
+			if (!tmp_pages[j])
+				goto free_pagearray;
+		}
+		ptr = vmap(tmp_pages, nrpages, VM_MAP, PAGE_KERNEL);
+		if (!ptr)
+			goto free_pagearray;
+
+		pages = tmp_pages;
+		spin_lock(&gbuf->lock);
+		old_ptr = gbuf->ptr;
+		gbuf->ptr = ptr;
+		tmp_pages = gbuf->pages;
+		gbuf->pages = pages;
+		j = gbuf->nrpages;
+		gbuf->nrpages = nrpages;
+		spin_unlock(&gbuf->lock);
+		ret = 0;
+		if (!tmp_pages) {
+			DBG_BUGON(old_ptr);
+			continue;
+		}
+
+		if (old_ptr)
+			vunmap(old_ptr);
+free_pagearray:
+		while (j)
+			erofs_pagepool_add(&pagepool, tmp_pages[--j]);
+		kfree(tmp_pages);
+		if (ret)
+			break;
+	}
+	z_erofs_gbuf_nrpages = nrpages;
+	erofs_release_pages(&pagepool);
+out:
+	mutex_unlock(&gbuf_resize_mutex);
+	return ret;
+}
+
+int __init z_erofs_gbuf_init(void)
+{
+	unsigned int i = num_possible_cpus();
+
+	if (!z_erofs_gbuf_count)
+		z_erofs_gbuf_count = i;
+	else
+		z_erofs_gbuf_count = min(z_erofs_gbuf_count, i);
+
+	z_erofs_gbufpool = kcalloc(z_erofs_gbuf_count,
+			sizeof(*z_erofs_gbufpool), GFP_KERNEL);
+	if (!z_erofs_gbufpool)
+		return -ENOMEM;
+
+	for (i = 0; i < z_erofs_gbuf_count; ++i)
+		spin_lock_init(&z_erofs_gbufpool[i].lock);
+	return 0;
+}
+
+void z_erofs_gbuf_exit(void)
+{
+	int i;
+
+	for (i = 0; i < z_erofs_gbuf_count; ++i) {
+		struct z_erofs_gbuf *gbuf = &z_erofs_gbufpool[i];
+
+		if (gbuf->ptr) {
+			vunmap(gbuf->ptr);
+			gbuf->ptr = NULL;
+		}
+
+		if (!gbuf->pages)
+			continue;
+
+		for (i = 0; i < gbuf->nrpages; ++i)
+			if (gbuf->pages[i])
+				put_page(gbuf->pages[i]);
+		kfree(gbuf->pages);
+		gbuf->pages = NULL;
+	}
+	kfree(z_erofs_gbufpool);
+}
+
 struct page *erofs_allocpage(struct page **pagepool, gfp_t gfp)
 {
 	struct page *page = *pagepool;