shmem: prepare huge= mount option and sysfs knob

This patch adds new mount option "huge=".  It can have following values:

  - "always":
	Attempt to allocate huge pages every time we need a new page;

  - "never":
	Do not allocate huge pages;

  - "within_size":
	Only allocate huge page if it will be fully within i_size.
	Also respect fadvise()/madvise() hints;

  - "advise:
	Only allocate huge pages if requested with fadvise()/madvise();

Default is "never" for now.

"mount -o remount,huge= /mountpoint" works fine after mount: remounting
huge=never will not attempt to break up huge pages at all, just stop
more from being allocated.

No new config option: put this under CONFIG_TRANSPARENT_HUGEPAGE, which
is the appropriate option to protect those who don't want the new bloat,
and with which we shall share some pmd code.

Prohibit the option when !CONFIG_TRANSPARENT_HUGEPAGE, just as mpol is
invalid without CONFIG_NUMA (was hidden in mpol_parse_str(): make it
explicit).

Allow enabling THP only if the machine has_transparent_hugepage().

But what about Shmem with no user-visible mount? SysV SHM, memfds,
shared anonymous mmaps (of /dev/zero or MAP_ANONYMOUS), GPU drivers' DRM
objects, Ashmem.  Though unlikely to suit all usages, provide sysfs knob
/sys/kernel/mm/transparent_hugepage/shmem_enabled to experiment with
huge on those.

And allow shmem_enabled two further values:

  - "deny":
	For use in emergencies, to force the huge option off from
	all mounts;
  - "force":
	Force the huge option on for all - very useful for testing;

Based on patch by Hugh Dickins.

Link: http://lkml.kernel.org/r/1466021202-61880-28-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 254aac4..2f75713 100644 (file)
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -41,6 +41,8 @@ enum transparent_hugepage_flag {
 #endif
 };
 
+extern struct kobj_attribute shmem_enabled_attr;
+
 #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
 #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
 

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 4d4780c..466f18c 100644 (file)
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -28,9 +28,10 @@ struct shmem_sb_info {
        unsigned long max_inodes;   /* How many inodes are allowed */
        unsigned long free_inodes;  /* How many are left for allocation */
        spinlock_t stat_lock;       /* Serialize shmem_sb_info changes */
+       umode_t mode;               /* Mount mode for root directory */
+       unsigned char huge;         /* Whether to try for hugepages */
        kuid_t uid;                 /* Mount uid for root directory */
        kgid_t gid;                 /* Mount gid for root directory */
-       umode_t mode;               /* Mount mode for root directory */
        struct mempolicy *mpol;     /* default memory policy for mappings */
 };
 

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 6c52498..cabd53d 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -442,6 +442,9 @@ static struct attribute *hugepage_attr[] = {
        &enabled_attr.attr,
        &defrag_attr.attr,
        &use_zero_page_attr.attr,
+#ifdef CONFIG_SHMEM
+       &shmem_enabled_attr.attr,
+#endif
 #ifdef CONFIG_DEBUG_VM
        &debug_cow_attr.attr,
 #endif

diff --git a/mm/shmem.c b/mm/shmem.c
index 171dee7..fd374f7 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -288,6 +288,87 @@ static bool shmem_confirm_swap(struct address_space *mapping,
        return item == swp_to_radix_entry(swap);
 }
 
+/*
+ * Definitions for "huge tmpfs": tmpfs mounted with the huge= option
+ *
+ * SHMEM_HUGE_NEVER:
+ *     disables huge pages for the mount;
+ * SHMEM_HUGE_ALWAYS:
+ *     enables huge pages for the mount;
+ * SHMEM_HUGE_WITHIN_SIZE:
+ *     only allocate huge pages if the page will be fully within i_size,
+ *     also respect fadvise()/madvise() hints;
+ * SHMEM_HUGE_ADVISE:
+ *     only allocate huge pages if requested with fadvise()/madvise();
+ */
+
+#define SHMEM_HUGE_NEVER       0
+#define SHMEM_HUGE_ALWAYS      1
+#define SHMEM_HUGE_WITHIN_SIZE 2
+#define SHMEM_HUGE_ADVISE      3
+
+/*
+ * Special values.
+ * Only can be set via /sys/kernel/mm/transparent_hugepage/shmem_enabled:
+ *
+ * SHMEM_HUGE_DENY:
+ *     disables huge on shm_mnt and all mounts, for emergency use;
+ * SHMEM_HUGE_FORCE:
+ *     enables huge on shm_mnt and all mounts, w/o needing option, for testing;
+ *
+ */
+#define SHMEM_HUGE_DENY                (-1)
+#define SHMEM_HUGE_FORCE       (-2)
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+/* ifdef here to avoid bloating shmem.o when not necessary */
+
+int shmem_huge __read_mostly;
+
+static int shmem_parse_huge(const char *str)
+{
+       if (!strcmp(str, "never"))
+               return SHMEM_HUGE_NEVER;
+       if (!strcmp(str, "always"))
+               return SHMEM_HUGE_ALWAYS;
+       if (!strcmp(str, "within_size"))
+               return SHMEM_HUGE_WITHIN_SIZE;
+       if (!strcmp(str, "advise"))
+               return SHMEM_HUGE_ADVISE;
+       if (!strcmp(str, "deny"))
+               return SHMEM_HUGE_DENY;
+       if (!strcmp(str, "force"))
+               return SHMEM_HUGE_FORCE;
+       return -EINVAL;
+}
+
+static const char *shmem_format_huge(int huge)
+{
+       switch (huge) {
+       case SHMEM_HUGE_NEVER:
+               return "never";
+       case SHMEM_HUGE_ALWAYS:
+               return "always";
+       case SHMEM_HUGE_WITHIN_SIZE:
+               return "within_size";
+       case SHMEM_HUGE_ADVISE:
+               return "advise";
+       case SHMEM_HUGE_DENY:
+               return "deny";
+       case SHMEM_HUGE_FORCE:
+               return "force";
+       default:
+               VM_BUG_ON(1);
+               return "bad_val";
+       }
+}
+
+#else /* !CONFIG_TRANSPARENT_HUGEPAGE */
+
+#define shmem_huge SHMEM_HUGE_DENY
+
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
 /*
  * Like add_to_page_cache_locked, but error if expected item has gone.
  */
@@ -2860,11 +2941,24 @@ static int shmem_parse_options(char *options, struct shmem_sb_info *sbinfo,
                        sbinfo->gid = make_kgid(current_user_ns(), gid);
                        if (!gid_valid(sbinfo->gid))
                                goto bad_val;
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+               } else if (!strcmp(this_char, "huge")) {
+                       int huge;
+                       huge = shmem_parse_huge(value);
+                       if (huge < 0)
+                               goto bad_val;
+                       if (!has_transparent_hugepage() &&
+                                       huge != SHMEM_HUGE_NEVER)
+                               goto bad_val;
+                       sbinfo->huge = huge;
+#endif
+#ifdef CONFIG_NUMA
                } else if (!strcmp(this_char,"mpol")) {
                        mpol_put(mpol);
                        mpol = NULL;
                        if (mpol_parse_str(value, &mpol))
                                goto bad_val;
+#endif
                } else {
                        pr_err("tmpfs: Bad mount option %s\n", this_char);
                        goto error;
@@ -2910,6 +3004,7 @@ static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
                goto out;
 
        error = 0;
+       sbinfo->huge = config.huge;
        sbinfo->max_blocks  = config.max_blocks;
        sbinfo->max_inodes  = config.max_inodes;
        sbinfo->free_inodes = config.max_inodes - inodes;
@@ -2943,6 +3038,11 @@ static int shmem_show_options(struct seq_file *seq, struct dentry *root)
        if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
                seq_printf(seq, ",gid=%u",
                                from_kgid_munged(&init_user_ns, sbinfo->gid));
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+       /* Rightly or wrongly, show huge mount option unmasked by shmem_huge */
+       if (sbinfo->huge)
+               seq_printf(seq, ",huge=%s", shmem_format_huge(sbinfo->huge));
+#endif
        shmem_show_mpol(seq, sbinfo->mpol);
        return 0;
 }
@@ -3282,6 +3382,13 @@ int __init shmem_init(void)
                pr_err("Could not kern_mount tmpfs\n");
                goto out1;
        }
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+       if (has_transparent_hugepage() && shmem_huge < SHMEM_HUGE_DENY)
+               SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
+       else
+               shmem_huge = 0; /* just in case it was patched */
+#endif
        return 0;
 
 out1:
@@ -3293,6 +3400,60 @@ out3:
        return error;
 }
 
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_SYSFS)
+static ssize_t shmem_enabled_show(struct kobject *kobj,
+               struct kobj_attribute *attr, char *buf)
+{
+       int values[] = {
+               SHMEM_HUGE_ALWAYS,
+               SHMEM_HUGE_WITHIN_SIZE,
+               SHMEM_HUGE_ADVISE,
+               SHMEM_HUGE_NEVER,
+               SHMEM_HUGE_DENY,
+               SHMEM_HUGE_FORCE,
+       };
+       int i, count;
+
+       for (i = 0, count = 0; i < ARRAY_SIZE(values); i++) {
+               const char *fmt = shmem_huge == values[i] ? "[%s] " : "%s ";
+
+               count += sprintf(buf + count, fmt,
+                               shmem_format_huge(values[i]));
+       }
+       buf[count - 1] = '\n';
+       return count;
+}
+
+static ssize_t shmem_enabled_store(struct kobject *kobj,
+               struct kobj_attribute *attr, const char *buf, size_t count)
+{
+       char tmp[16];
+       int huge;
+
+       if (count + 1 > sizeof(tmp))
+               return -EINVAL;
+       memcpy(tmp, buf, count);
+       tmp[count] = '\0';
+       if (count && tmp[count - 1] == '\n')
+               tmp[count - 1] = '\0';
+
+       huge = shmem_parse_huge(tmp);
+       if (huge == -EINVAL)
+               return -EINVAL;
+       if (!has_transparent_hugepage() &&
+                       huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY)
+               return -EINVAL;
+
+       shmem_huge = huge;
+       if (shmem_huge < SHMEM_HUGE_DENY)
+               SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
+       return count;
+}
+
+struct kobj_attribute shmem_enabled_attr =
+       __ATTR(shmem_enabled, 0644, shmem_enabled_show, shmem_enabled_store);
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE && CONFIG_SYSFS */
+
 #else /* !CONFIG_SHMEM */
 
 /*