From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joel Becker Date: Fri, 21 Aug 2009 11:39:44 -0700 Subject: [Ocfs2-devel] [PATCH 17/41] ocfs2: Add CoW support. In-Reply-To: <1250843065-6381-1-git-send-email-tao.ma@oracle.com> References: <20090821070737.GB20755@mail.oracle.com> <1250843065-6381-1-git-send-email-tao.ma@oracle.com> Message-ID: <20090821183944.GA4330@mail.oracle.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ocfs2-devel@oss.oracle.com On Fri, Aug 21, 2009 at 04:24:25PM +0800, Tao Ma wrote: > As our talk in irc, here is the updated one. Please review. Perfect. Here's a version with the math wrapped in shiny readable inlines. Some comments were updated too. I didn't actually change the logic, so please verify I got it right. Joel diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c index d59860d..8f0d210 100644 --- a/fs/ocfs2/refcounttree.c +++ b/fs/ocfs2/refcounttree.c @@ -2499,7 +2499,52 @@ out: return ret; } -#define MAX_COW_BYTES 1048576 +#define MAX_CONTIG_BYTES 1048576 + +static inline unsigned int ocfs2_cow_contig_clusters(struct super_block *sb) +{ + return ocfs2_clusters_for_bytes(sb, MAX_CONTIG_BYTES); +} + +static inline unsigned int ocfs2_cow_contig_mask(struct super_block *sb) +{ + return ~(ocfs2_cow_contig_clusters(sb) - 1); +} + +/* + * Given an extent that starts at 'start and an I/O that starts at + * 'cpos, find an offset (start * (n * contig_clusters)) that is closest + * to cpos while still being less than or equal to it. + * + * The goal is to break the extent at a multiple of contig_clusters. + */ +static inline unsigned int ocfs2_cow_align_start(struct super_block *sb, + unsigned int start, + unsigned int cpos) +{ + BUG_ON(start > cpos); + + return start + ((cpos - start) & ocfs2_cow_contig_mask(sb)); +} + +/* + * Given a cluster count of len, pad it out so that it is a multiple + * of contig_clusters. + */ +static inline unsigned int ocfs2_cow_align_length(struct super_block *sb, + unsigned int len) +{ + unsigned int padded = + (len + (ocfs2_cow_contig_clusters(sb) - 1)) & + ocfs2_cow_contig_mask(sb); + + /* Did we wrap? */ + if (padded < len) + padded = UINT_MAX; + + return padded; +} + /* * Calculate out the start and number of virtual clusters we need to to CoW. * @@ -2508,9 +2553,8 @@ out: * max_cpos is the place where we want to stop CoW intentionally. * * Normal we will start CoW from the beginning of extent record cotaining cpos. - * And We will try to Cow as much clusters as we can until we reach - * MAX_COW_BYTES. If the write_len is larger than MAX_COW_BYTES, we will - * use that value as the maximum clusters. + * We try to break up extents on boundaries of MAX_CONTIG_BYTES so that we + * get good I/O from the resulting extent tree. */ static int ocfs2_refcount_cal_cow_clusters(struct inode *inode, struct ocfs2_extent_list *el, @@ -2525,10 +2569,10 @@ static int ocfs2_refcount_cal_cow_clusters(struct inode *inode, struct buffer_head *eb_bh = NULL; struct ocfs2_extent_block *eb = NULL; struct ocfs2_extent_rec *rec; - int max_clusters = ocfs2_clusters_for_bytes(inode->i_sb, MAX_COW_BYTES); - int leaf_clusters, rec_end = 0; + unsigned int want_clusters, rec_end = 0; + int contig_clusters = ocfs2_cow_contig_clusters(inode->i_sb); + int leaf_clusters; - max_clusters = max_clusters < write_len ? write_len : max_clusters; if (tree_height > 0) { ret = ocfs2_find_leaf(INODE_CACHE(inode), el, cpos, &eb_bh); if (ret) { @@ -2587,53 +2631,98 @@ static int ocfs2_refcount_cal_cow_clusters(struct inode *inode, leaf_clusters = rec_end - le32_to_cpu(rec->e_cpos); } - if (*cow_len + leaf_clusters >= max_clusters) { - if (*cow_len == 0) { - /* - * cpos is in a very large extent record. - * So just split max_clusters from the - * extent record. - */ - if ((rec_end - cpos) <= max_clusters) { - /* - * We can take max_clusters off - * the end and cover all of our - * write. - */ - *cow_start = rec_end - max_clusters; - } else if ((*cow_start + max_clusters) > - (cpos + write_len)) { - /* - * We can take max_clusters off - * the front and cover all of - * our write. - */ - /* NOOP, *cow_start is already set */ - } else { - /* - * We're CoWing more data than - * write_len for contiguousness, - * but it doesn't fit at the - * front or end of this extent. - * Let's try to slice the extent - * up nicely. Optimally, our - * CoW region starts at a - * multiple of max_clusters. If - * that doesn't fit, we give up - * and just CoW at cpos. - */ - *cow_start += - (cpos - *cow_start) & - ~(max_clusters - 1); - if ((*cow_start + max_clusters) < - (cpos + write_len)) - *cow_start = cpos; - } - } - *cow_len = max_clusters; - break; - } else + /* + * How many clusters do we actually need from + * this extent? First we see how many we actually + * need to complete the write. If that's smaller + * than contig_clusters, we try for contig_clusters. + */ + if (!*cow_len) + want_clusters = write_len; + else + want_clusters = (cpos + write_len) - + (*cow_start + *cow_len); + if (want_clusters < contig_clusters) + want_clusters = contig_clusters; + + /* + * If the write does not cover the whole extent, we + * need to calculate how we're going to split the extent. + * We try to do it on contig_clusters boundaries. + * + * Any extent smaller than contig_clusters will be + * CoWed in its entirety. + */ + if (leaf_clusters <= contig_clusters) *cow_len += leaf_clusters; + else if (*cow_len || (*cow_start == cpos)) { + /* + * This extent needs to be CoW'd from its + * beginning, so all we have to do is compute + * how many clusters to grab. We align + * want_clusters to the edge of contig_clusters + * to get better I/O. + */ + want_clusters = ocfs2_cow_align_length(inode->i_sb, + want_clusters); + + if (leaf_clusters < want_clusters) + *cow_len += leaf_clusters; + else + *cow_len += want_clusters; + } else if ((*cow_start + contig_clusters) >= + (cpos + write_len)) { + /* + * Breaking off contig_clusters at the front + * of the extent will cover our write. That's + * easy. + */ + *cow_len = contig_clusters; + } else if ((rec_end - cpos) <= contig_clusters) { + /* + * Breaking off contig_clusters at the tail of + * this extent will cover cpos. + */ + *cow_start = rec_end - cpos; + *cow_len = contig_clusters; + } else if ((rec_end - cpos) <= want_clusters) { + /* + * While we can't fit the entire write in this + * extent, we know that the write goes from cpos + * to the end of the extent. Break that off. + * We try to break it@some multiple of + * contig_clusters from the front of the extent. + * Failing that (ie, cpos is within + * contig_clusters of the front), we'll CoW the + * entire extent. + */ + *cow_start = ocfs2_cow_align_start(inode->i_sb, + *cow_start, cpos); + *cow_len = rec_end - *cow_start; + } else { + /* + * Ok, the entire write lives in the middle of + * this extent. Let's try to slice the extent up + * nicely. Optimally, our CoW region starts at + * m*contig_clusters from the beginning of the + * extent and goes for n*contig_clusters, + * covering the entire write. + */ + *cow_start = ocfs2_cow_align_start(inode->i_sb, + *cow_start, cpos); + + want_clusters = (cpos + write_len) - *cow_start; + want_clusters = ocfs2_cow_align_length(inode->i_sb, + want_clusters); + if (*cow_start + want_clusters <= rec_end) + *cow_len = want_clusters; + else + *cow_len = rec_end - *cow_start; + } + + /* Have we covered our entire write yet? */ + if ((*cow_start + *cow_len) >= (cpos + write_len)) + break; /* * If we reach the end of the extent block and don't get enough -- "Any man who is under 30, and is not a liberal, has not heart; and any man who is over 30, and is not a conservative, has no brains." - Sir Winston Churchill Joel Becker Principal Software Developer Oracle E-mail: joel.becker at oracle.com Phone: (650) 506-8127