diff options
Diffstat (limited to 'fs/xfs/xfs_iwalk.c')
| -rw-r--r-- | fs/xfs/xfs_iwalk.c | 48 |
1 files changed, 45 insertions, 3 deletions
diff --git a/fs/xfs/xfs_iwalk.c b/fs/xfs/xfs_iwalk.c index 304c41e6ed1d..4aa22f02b9ec 100644 --- a/fs/xfs/xfs_iwalk.c +++ b/fs/xfs/xfs_iwalk.c @@ -334,15 +334,57 @@ out: } /* + * We experimentally determined that the reduction in ioctl call overhead + * diminishes when userspace asks for more than 2048 inodes, so we'll cap + * prefetch at this point. + */ +#define IWALK_MAX_INODE_PREFETCH (2048U) + +/* * Given the number of inodes to prefetch, set the number of inobt records that * we cache in memory, which controls the number of inodes we try to read - * ahead. + * ahead. Set the maximum if @inodes == 0. */ static inline unsigned int xfs_iwalk_prefetch( - unsigned int inode_records) + unsigned int inodes) { - return PAGE_SIZE * 4 / sizeof(struct xfs_inobt_rec_incore); + unsigned int inobt_records; + + /* + * If the caller didn't tell us the number of inodes they wanted, + * assume the maximum prefetch possible for best performance. + * Otherwise, cap prefetch at that maximum so that we don't start an + * absurd amount of prefetch. + */ + if (inodes == 0) + inodes = IWALK_MAX_INODE_PREFETCH; + inodes = min(inodes, IWALK_MAX_INODE_PREFETCH); + + /* Round the inode count up to a full chunk. */ + inodes = round_up(inodes, XFS_INODES_PER_CHUNK); + + /* + * In order to convert the number of inodes to prefetch into an + * estimate of the number of inobt records to cache, we require a + * conversion factor that reflects our expectations of the average + * loading factor of an inode chunk. Based on data gathered, most + * (but not all) filesystems manage to keep the inode chunks totally + * full, so we'll underestimate slightly so that our readahead will + * still deliver the performance we want on aging filesystems: + * + * inobt = inodes / (INODES_PER_CHUNK * (4 / 5)); + * + * The funny math is to avoid integer division. + */ + inobt_records = (inodes * 5) / (4 * XFS_INODES_PER_CHUNK); + + /* + * Allocate enough space to prefetch at least two inobt records so that + * we can cache both the record where the iwalk started and the next + * record. This simplifies the AG inode walk loop setup code. + */ + return max(inobt_records, 2U); } /* |