Add a helper to do the pre-reading work for the netfs write_begin address space op.
Changes v6: - Fixed a missing rreq put in netfs_write_begin()[3]. - Use DEFINE_READAHEAD()[4]. v5: - Made the wait for PG_fscache in netfs_write_begin() killable[2]. v4: - Added flag to netfs_subreq_terminated() to indicate that the caller may have been running async and stuff that might sleep needs punting to a workqueue (can't use in_softirq()[1]). Signed-off-by: David Howells <dhowe...@redhat.com> Reviewed-by: Jeff Layton <jlay...@redhat.com> cc: Matthew Wilcox <wi...@infradead.org> cc: linux...@kvack.org cc: linux-cach...@redhat.com cc: linux-...@lists.infradead.org cc: linux-...@vger.kernel.org cc: linux-c...@vger.kernel.org cc: ceph-de...@vger.kernel.org cc: v9fs-develo...@lists.sourceforge.net cc: linux-fsde...@vger.kernel.org Link: https://lore.kernel.org/r/20210216084230.ga23...@lst.de/ [1] Link: https://lore.kernel.org/r/2499407.1616505...@warthog.procyon.org.uk/ [2] Link: https://lore.kernel.org/r/161781042127.463527.9154479794406046987.st...@warthog.procyon.org.uk/ [3] Link: https://lore.kernel.org/r/1234933.1617886...@warthog.procyon.org.uk/ [4] Link: https://lore.kernel.org/r/160588543960.3465195.2792938973035886168.st...@warthog.procyon.org.uk/ # rfc Link: https://lore.kernel.org/r/161118140165.1232039.16418853874312234477.st...@warthog.procyon.org.uk/ # rfc Link: https://lore.kernel.org/r/161161035539.2537118.15674887534950908530.st...@warthog.procyon.org.uk/ # v2 Link: https://lore.kernel.org/r/161340398368.1303470.11242918276563276090.st...@warthog.procyon.org.uk/ # v3 Link: https://lore.kernel.org/r/161539541541.286939.1889738674057013729.st...@warthog.procyon.org.uk/ # v4 Link: https://lore.kernel.org/r/161653798616.2770958.17213315845968485563.st...@warthog.procyon.org.uk/ # v5 --- fs/netfs/internal.h | 2 + fs/netfs/read_helper.c | 164 ++++++++++++++++++++++++++++++++++++++++++ fs/netfs/stats.c | 11 ++- include/linux/netfs.h | 8 ++ include/trace/events/netfs.h | 4 + 5 files changed, 185 insertions(+), 4 deletions(-) diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h index 98b6f4516da1..b7f2c4459f33 100644 --- a/fs/netfs/internal.h +++ b/fs/netfs/internal.h @@ -34,8 +34,10 @@ extern atomic_t netfs_n_rh_read_failed; extern atomic_t netfs_n_rh_zero; extern atomic_t netfs_n_rh_short_read; extern atomic_t netfs_n_rh_write; +extern atomic_t netfs_n_rh_write_begin; extern atomic_t netfs_n_rh_write_done; extern atomic_t netfs_n_rh_write_failed; +extern atomic_t netfs_n_rh_write_zskip; static inline void netfs_stat(atomic_t *stat) diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c index 6d6ed30f417e..da34aedea053 100644 --- a/fs/netfs/read_helper.c +++ b/fs/netfs/read_helper.c @@ -772,3 +772,167 @@ int netfs_readpage(struct file *file, return ret; } EXPORT_SYMBOL(netfs_readpage); + +static void netfs_clear_thp(struct page *page) +{ + unsigned int i; + + for (i = 0; i < thp_nr_pages(page); i++) + clear_highpage(page + i); +} + +/** + * netfs_write_begin - Helper to prepare for writing + * @file: The file to read from + * @mapping: The mapping to read from + * @pos: File position at which the write will begin + * @len: The length of the write in this page + * @flags: AOP_* flags + * @_page: Where to put the resultant page + * @_fsdata: Place for the netfs to store a cookie + * @ops: The network filesystem's operations for the helper to use + * @netfs_priv: Private netfs data to be retained in the request + * + * Pre-read data for a write-begin request by drawing data from the cache if + * possible, or the netfs if not. Space beyond the EOF is zero-filled. + * Multiple I/O requests from different sources will get munged together. If + * necessary, the readahead window can be expanded in either direction to a + * more convenient alighment for RPC efficiency or to make storage in the cache + * feasible. + * + * The calling netfs must provide a table of operations, only one of which, + * issue_op, is mandatory. + * + * The check_write_begin() operation can be provided to check for and flush + * conflicting writes once the page is grabbed and locked. It is passed a + * pointer to the fsdata cookie that gets returned to the VM to be passed to + * write_end. It is permitted to sleep. It should return 0 if the request + * should go ahead; unlock the page and return -EAGAIN to cause the page to be + * regot; or return an error. + * + * This is usable whether or not caching is enabled. + */ +int netfs_write_begin(struct file *file, struct address_space *mapping, + loff_t pos, unsigned int len, unsigned int flags, + struct page **_page, void **_fsdata, + const struct netfs_read_request_ops *ops, + void *netfs_priv) +{ + struct netfs_read_request *rreq; + struct page *page, *xpage; + struct inode *inode = file_inode(file); + unsigned int debug_index = 0; + pgoff_t index = pos >> PAGE_SHIFT; + int pos_in_page = pos & ~PAGE_MASK; + loff_t size; + int ret; + + DEFINE_READAHEAD(ractl, file, NULL, mapping, index); + +retry: + page = grab_cache_page_write_begin(mapping, index, 0); + if (!page) + return -ENOMEM; + + if (ops->check_write_begin) { + /* Allow the netfs (eg. ceph) to flush conflicts. */ + ret = ops->check_write_begin(file, pos, len, page, _fsdata); + if (ret < 0) { + if (ret == -EAGAIN) + goto retry; + goto error; + } + } + + if (PageUptodate(page)) + goto have_page; + + /* If the page is beyond the EOF, we want to clear it - unless it's + * within the cache granule containing the EOF, in which case we need + * to preload the granule. + */ + size = i_size_read(inode); + if (!ops->is_cache_enabled(inode) && + ((pos_in_page == 0 && len == thp_size(page)) || + (pos >= size) || + (pos_in_page == 0 && (pos + len) >= size))) { + netfs_clear_thp(page); + SetPageUptodate(page); + netfs_stat(&netfs_n_rh_write_zskip); + goto have_page_no_wait; + } + + ret = -ENOMEM; + rreq = netfs_alloc_read_request(ops, netfs_priv, file); + if (!rreq) + goto error; + rreq->mapping = page->mapping; + rreq->start = page->index * PAGE_SIZE; + rreq->len = thp_size(page); + rreq->no_unlock_page = page->index; + __set_bit(NETFS_RREQ_NO_UNLOCK_PAGE, &rreq->flags); + netfs_priv = NULL; + + netfs_stat(&netfs_n_rh_write_begin); + trace_netfs_read(rreq, pos, len, netfs_read_trace_write_begin); + + /* Expand the request to meet caching requirements and download + * preferences. + */ + ractl._nr_pages = thp_nr_pages(page); + netfs_rreq_expand(rreq, &ractl); + netfs_get_read_request(rreq); + + /* We hold the page locks, so we can drop the references */ + while ((xpage = readahead_page(&ractl))) + if (xpage != page) + put_page(xpage); + + atomic_set(&rreq->nr_rd_ops, 1); + do { + if (!netfs_rreq_submit_slice(rreq, &debug_index)) + break; + + } while (rreq->submitted < rreq->len); + + /* Keep nr_rd_ops incremented so that the ref always belongs to us, and + * the service code isn't punted off to a random thread pool to + * process. + */ + for (;;) { + wait_var_event(&rreq->nr_rd_ops, atomic_read(&rreq->nr_rd_ops) == 1); + netfs_rreq_assess(rreq, false); + if (!test_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags)) + break; + cond_resched(); + } + + ret = rreq->error; + if (ret == 0 && rreq->submitted < rreq->len) + ret = -EIO; + netfs_put_read_request(rreq, false); + if (ret < 0) + goto error; + +have_page: + ret = wait_on_page_fscache_killable(page); + if (ret < 0) + goto error; +have_page_no_wait: + if (netfs_priv) + ops->cleanup(netfs_priv, mapping); + *_page = page; + _leave(" = 0"); + return 0; + +error_put: + netfs_put_read_request(rreq, false); +error: + unlock_page(page); + put_page(page); + if (netfs_priv) + ops->cleanup(netfs_priv, mapping); + _leave(" = %d", ret); + return ret; +} +EXPORT_SYMBOL(netfs_write_begin); diff --git a/fs/netfs/stats.c b/fs/netfs/stats.c index df6ff5718f25..9ae538c85378 100644 --- a/fs/netfs/stats.c +++ b/fs/netfs/stats.c @@ -24,19 +24,24 @@ atomic_t netfs_n_rh_read_failed; atomic_t netfs_n_rh_zero; atomic_t netfs_n_rh_short_read; atomic_t netfs_n_rh_write; +atomic_t netfs_n_rh_write_begin; atomic_t netfs_n_rh_write_done; atomic_t netfs_n_rh_write_failed; +atomic_t netfs_n_rh_write_zskip; void netfs_stats_show(struct seq_file *m) { - seq_printf(m, "RdHelp : RA=%u RP=%u rr=%u sr=%u\n", + seq_printf(m, "RdHelp : RA=%u RP=%u WB=%u WBZ=%u rr=%u sr=%u\n", atomic_read(&netfs_n_rh_readahead), atomic_read(&netfs_n_rh_readpage), + atomic_read(&netfs_n_rh_write_begin), + atomic_read(&netfs_n_rh_write_zskip), atomic_read(&netfs_n_rh_rreq), atomic_read(&netfs_n_rh_sreq)); - seq_printf(m, "RdHelp : ZR=%u sh=%u\n", + seq_printf(m, "RdHelp : ZR=%u sh=%u sk=%u\n", atomic_read(&netfs_n_rh_zero), - atomic_read(&netfs_n_rh_short_read)); + atomic_read(&netfs_n_rh_short_read), + atomic_read(&netfs_n_rh_write_zskip)); seq_printf(m, "RdHelp : DL=%u ds=%u df=%u di=%u\n", atomic_read(&netfs_n_rh_download), atomic_read(&netfs_n_rh_download_done), diff --git a/include/linux/netfs.h b/include/linux/netfs.h index db4af80cbae3..99659ed9524e 100644 --- a/include/linux/netfs.h +++ b/include/linux/netfs.h @@ -147,11 +147,14 @@ struct netfs_read_request { * Operations the network filesystem can/must provide to the helpers. */ struct netfs_read_request_ops { + bool (*is_cache_enabled)(struct inode *inode); void (*init_rreq)(struct netfs_read_request *rreq, struct file *file); void (*expand_readahead)(struct netfs_read_request *rreq); bool (*clamp_length)(struct netfs_read_subrequest *subreq); void (*issue_op)(struct netfs_read_subrequest *subreq); bool (*is_still_valid)(struct netfs_read_request *rreq); + int (*check_write_begin)(struct file *file, loff_t pos, unsigned len, + struct page *page, void **_fsdata); void (*done)(struct netfs_read_request *rreq); void (*cleanup)(struct address_space *mapping, void *netfs_priv); }; @@ -164,6 +167,11 @@ extern int netfs_readpage(struct file *, struct page *, const struct netfs_read_request_ops *, void *); +extern int netfs_write_begin(struct file *, struct address_space *, + loff_t, unsigned int, unsigned int, struct page **, + void **, + const struct netfs_read_request_ops *, + void *); extern void netfs_subreq_terminated(struct netfs_read_subrequest *, ssize_t, bool); extern void netfs_stats_show(struct seq_file *); diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h index 12ad382764c5..a2bf6cd84bd4 100644 --- a/include/trace/events/netfs.h +++ b/include/trace/events/netfs.h @@ -22,6 +22,7 @@ enum netfs_read_trace { netfs_read_trace_expanded, netfs_read_trace_readahead, netfs_read_trace_readpage, + netfs_read_trace_write_begin, }; enum netfs_rreq_trace { @@ -50,7 +51,8 @@ enum netfs_sreq_trace { #define netfs_read_traces \ EM(netfs_read_trace_expanded, "EXPANDED ") \ EM(netfs_read_trace_readahead, "READAHEAD") \ - E_(netfs_read_trace_readpage, "READPAGE ") + EM(netfs_read_trace_readpage, "READPAGE ") \ + E_(netfs_read_trace_write_begin, "WRITEBEGN") #define netfs_rreq_traces \ EM(netfs_rreq_trace_assess, "ASSESS") \
