Return-Path: linux-nfs-owner@vger.kernel.org Received: from mail-ig0-f178.google.com ([209.85.213.178]:53639 "EHLO mail-ig0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758125AbaDXPXX convert rfc822-to-8bit (ORCPT ); Thu, 24 Apr 2014 11:23:23 -0400 Received: by mail-ig0-f178.google.com with SMTP id hn18so1021674igb.17 for ; Thu, 24 Apr 2014 08:23:22 -0700 (PDT) Content-Type: text/plain; charset=windows-1252 Mime-Version: 1.0 (Mac OS X Mail 7.2 \(1874\)) Subject: Re: [PATCH 05/17] nfs: add support for multiple nfs reqs per page From: Weston Andros Adamson In-Reply-To: <20140424105000.665c159e@tlielax.poochiereds.net> Date: Thu, 24 Apr 2014 11:23:19 -0400 Cc: Trond Myklebust , linux-nfs list Message-Id: <3DEC13E0-CC9B-498D-A97A-98D77628F672@primarydata.com> References: <1398202165-78897-1-git-send-email-dros@primarydata.com> <1398202165-78897-6-git-send-email-dros@primarydata.com> <20140424105000.665c159e@tlielax.poochiereds.net> To: Jeff Layton Sender: linux-nfs-owner@vger.kernel.org List-ID: On Apr 24, 2014, at 10:50 AM, Jeff Layton wrote: > On Tue, 22 Apr 2014 17:29:13 -0400 > Weston Andros Adamson wrote: > >> Add "page groups" - a circular list of nfs requests (struct nfs_page) >> that all reference the same page. This gives nfs read and write paths >> the ability to account for sub-page regions independently. This >> somewhat follows the design of struct buffer_head's sub-page >> accounting. >> >> Only "head" requests are ever added/removed from the inode list in >> the buffered write path. "head" and "sub" requests are treated the >> same through the read path and the rest of the write/commit path. >> Requests are given an extra reference across the life of the list. >> >> Page groups are never rejoined after being split. If the read/write >> request fails and the client falls back to another path (ie revert >> to MDS in PNFS case), the already split requests are pushed through >> the recoalescing code again, which may split them further and then >> coalesce them into properly sized requests on the wire. Fragmentation >> shouldn't be a problem with the current design, because we flush all >> requests in page group when a non-contiguous request is added, so >> the only time resplitting should occur is on a resend of a read or >> write. >> >> This patch lays the groundwork for sub-page splitting, but does not >> actually do any splitting. For now all page groups have one request >> as pg_test functions don't yet split pages. There are several related >> patches that are needed support multiple requests per page group. >> >> Signed-off-by: Weston Andros Adamson >> --- >> fs/nfs/direct.c | 7 +- >> fs/nfs/pagelist.c | 218 ++++++++++++++++++++++++++++++++++++++++++++--- >> fs/nfs/read.c | 4 +- >> fs/nfs/write.c | 12 ++- >> include/linux/nfs_page.h | 12 ++- >> 5 files changed, 231 insertions(+), 22 deletions(-) >> >> diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c >> index a0c30c5..9d968ca 100644 >> --- a/fs/nfs/direct.c >> +++ b/fs/nfs/direct.c >> @@ -380,7 +380,7 @@ static ssize_t nfs_direct_read_schedule_segment(struct nfs_pageio_descriptor *de >> struct nfs_page *req; >> unsigned int req_len = min_t(size_t, bytes, PAGE_SIZE - pgbase); >> /* XXX do we need to do the eof zeroing found in async_filler? */ >> - req = nfs_create_request(dreq->ctx, pagevec[i], >> + req = nfs_create_request(dreq->ctx, pagevec[i], NULL, >> pgbase, req_len); >> if (IS_ERR(req)) { >> result = PTR_ERR(req); >> @@ -749,7 +749,7 @@ static ssize_t nfs_direct_write_schedule_segment(struct nfs_pageio_descriptor *d >> struct nfs_page *req; >> unsigned int req_len = min_t(size_t, bytes, PAGE_SIZE - pgbase); >> >> - req = nfs_create_request(dreq->ctx, pagevec[i], >> + req = nfs_create_request(dreq->ctx, pagevec[i], NULL, >> pgbase, req_len); >> if (IS_ERR(req)) { >> result = PTR_ERR(req); >> @@ -827,6 +827,8 @@ static void nfs_direct_write_completion(struct nfs_pgio_header *hdr) >> spin_unlock(&dreq->lock); >> >> while (!list_empty(&hdr->pages)) { >> + bool do_destroy = true; >> + >> req = nfs_list_entry(hdr->pages.next); >> nfs_list_remove_request(req); >> switch (bit) { >> @@ -834,6 +836,7 @@ static void nfs_direct_write_completion(struct nfs_pgio_header *hdr) >> case NFS_IOHDR_NEED_COMMIT: >> kref_get(&req->wb_kref); >> nfs_mark_request_commit(req, hdr->lseg, &cinfo); >> + do_destroy = false; >> } >> nfs_unlock_and_release_request(req); >> } >> diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c >> index ac4fb64..8cb8e14 100644 >> --- a/fs/nfs/pagelist.c >> +++ b/fs/nfs/pagelist.c >> @@ -26,6 +26,8 @@ >> >> static struct kmem_cache *nfs_page_cachep; >> >> +static void nfs_free_request(struct nfs_page *); >> + >> bool nfs_pgarray_set(struct nfs_page_array *p, unsigned int pagecount) >> { >> p->npages = pagecount; >> @@ -133,10 +135,145 @@ nfs_iocounter_wait(struct nfs_io_counter *c) >> return __nfs_iocounter_wait(c); >> } >> >> +/* >> + * nfs_page_group_lock - lock the head of the page group >> + * @req - request in group that is to be locked >> + * >> + * this lock must be held if modifying the page group list >> + */ >> +void >> +nfs_page_group_lock(struct nfs_page *req) >> +{ >> + struct nfs_page *head = req->wb_head; >> + int err = -EAGAIN; >> + >> + WARN_ON_ONCE(head != head->wb_head); >> + >> + while (err) >> + err = wait_on_bit_lock(&head->wb_flags, PG_HEADLOCK, >> + nfs_wait_bit_killable, TASK_KILLABLE); >> +} >> + >> +/* >> + * nfs_page_group_unlock - unlock the head of the page group >> + * @req - request in group that is to be unlocked >> + */ >> +void >> +nfs_page_group_unlock(struct nfs_page *req) >> +{ >> + struct nfs_page *head = req->wb_head; >> + >> + WARN_ON_ONCE(head != head->wb_head); >> + >> + smp_mb__before_clear_bit(); >> + clear_bit(PG_HEADLOCK, &head->wb_flags); >> + smp_mb__after_clear_bit(); >> + wake_up_bit(&head->wb_flags, PG_HEADLOCK); >> +} >> + >> +/* >> + * nfs_page_group_sync_on_bit_locked >> + * >> + * must be called with page group lock held >> + */ >> +static bool >> +nfs_page_group_sync_on_bit_locked(struct nfs_page *req, unsigned int bit) >> +{ >> + struct nfs_page *head = req->wb_head; >> + struct nfs_page *tmp; >> + >> + WARN_ON_ONCE(!test_bit(PG_HEADLOCK, &head->wb_flags)); >> + WARN_ON_ONCE(test_and_set_bit(bit, &req->wb_flags)); >> + >> + tmp = req->wb_this_page; >> + while (tmp != req) { >> + if (!test_bit(bit, &tmp->wb_flags)) >> + return false; >> + tmp = tmp->wb_this_page; >> + } >> + >> + /* true! reset all bits */ >> + tmp = req; >> + do { >> + clear_bit(bit, &tmp->wb_flags); >> + tmp = tmp->wb_this_page; >> + } while (tmp != req); >> + >> + return true; >> +} >> + >> +/* >> + * nfs_page_group_sync_on_bit - set bit on current request, but only >> + * return true if the bit is set for all requests in page group >> + * @req - request in page group >> + * @bit - PG_* bit that is used to sync page group >> + */ >> +bool nfs_page_group_sync_on_bit(struct nfs_page *req, unsigned int bit) >> +{ >> + bool ret; >> + >> + nfs_page_group_lock(req); >> + ret = nfs_page_group_sync_on_bit_locked(req, bit); >> + nfs_page_group_unlock(req); >> + >> + return ret; >> +} >> + >> +/* >> + * nfs_page_group_init - Initialize the page group linkage for @req >> + * @req - a new nfs request >> + * @prev - the previous request in page group, or NULL if @req is the first >> + * or only request in the group (the head). >> + */ >> +static inline void >> +nfs_page_group_init(struct nfs_page *req, struct nfs_page *prev) >> +{ >> + WARN_ON_ONCE(prev == req); >> + >> + if (!prev) { >> + req->wb_head = req; >> + req->wb_this_page = req; >> + } else { >> + WARN_ON_ONCE(prev->wb_this_page != prev->wb_head); >> + WARN_ON_ONCE(!test_bit(PG_HEADLOCK, &prev->wb_head->wb_flags)); >> + req->wb_head = prev->wb_head; >> + req->wb_this_page = prev->wb_this_page; >> + prev->wb_this_page = req; >> + } >> +} >> + >> +/* >> + * nfs_page_group_destroy - sync the destruction of page groups >> + * @req - request that no longer needs the page group >> + * >> + * releases the page group reference from each member once all >> + * members have called this function. >> + */ >> +static void >> +nfs_page_group_destroy(struct kref *kref) >> +{ >> + struct nfs_page *req = container_of(kref, struct nfs_page, wb_kref); >> + struct nfs_page *tmp, *next; >> + >> + if (!nfs_page_group_sync_on_bit(req, PG_TEARDOWN)) >> + return; >> + >> + tmp = req; >> + do { >> + next = tmp->wb_this_page; >> + /* unlink and free */ >> + tmp->wb_this_page = tmp; >> + tmp->wb_head = tmp; >> + nfs_free_request(tmp); >> + tmp = next; >> + } while (tmp != req); >> +} >> + >> /** >> * nfs_create_request - Create an NFS read/write request. >> * @ctx: open context to use >> * @page: page to write >> + * @last: last nfs request created for this page group or NULL if head >> * @offset: starting offset within the page for the write >> * @count: number of bytes to read/write >> * >> @@ -146,7 +283,8 @@ nfs_iocounter_wait(struct nfs_io_counter *c) >> */ >> struct nfs_page * >> nfs_create_request(struct nfs_open_context *ctx, struct page *page, >> - unsigned int offset, unsigned int count) >> + struct nfs_page *last, unsigned int offset, >> + unsigned int count) >> { >> struct nfs_page *req; >> struct nfs_lock_context *l_ctx; >> @@ -178,6 +316,7 @@ nfs_create_request(struct nfs_open_context *ctx, struct page *page, >> req->wb_bytes = count; >> req->wb_context = get_nfs_open_context(ctx); >> kref_init(&req->wb_kref); >> + nfs_page_group_init(req, last); >> return req; >> } >> >> @@ -235,16 +374,22 @@ static void nfs_clear_request(struct nfs_page *req) >> } >> } >> >> - >> /** >> * nfs_release_request - Release the count on an NFS read/write request >> * @req: request to release >> * >> * Note: Should never be called with the spinlock held! >> */ >> -static void nfs_free_request(struct kref *kref) >> +static void nfs_free_request(struct nfs_page *req) >> { >> - struct nfs_page *req = container_of(kref, struct nfs_page, wb_kref); >> + WARN_ON_ONCE(req->wb_this_page != req); >> + >> + /* extra debug: make sure no sync bits are still set */ >> + WARN_ON_ONCE(test_bit(PG_TEARDOWN, &req->wb_flags)); >> + WARN_ON_ONCE(test_bit(PG_UNLOCKPAGE, &req->wb_flags)); >> + WARN_ON_ONCE(test_bit(PG_UPTODATE, &req->wb_flags)); >> + WARN_ON_ONCE(test_bit(PG_WB_END, &req->wb_flags)); >> + WARN_ON_ONCE(test_bit(PG_REMOVE, &req->wb_flags)); >> >> /* Release struct file and open context */ >> nfs_clear_request(req); >> @@ -253,7 +398,7 @@ static void nfs_free_request(struct kref *kref) >> >> void nfs_release_request(struct nfs_page *req) >> { >> - kref_put(&req->wb_kref, nfs_free_request); >> + kref_put(&req->wb_kref, nfs_page_group_destroy); >> } >> >> static int nfs_wait_bit_uninterruptible(void *word) >> @@ -439,21 +584,66 @@ static void nfs_pageio_doio(struct nfs_pageio_descriptor *desc) >> * @desc: destination io descriptor >> * @req: request >> * >> + * This may split a request into subrequests which are all part of the >> + * same page group. >> + * >> * Returns true if the request 'req' was successfully coalesced into the >> * existing list of pages 'desc'. >> */ >> static int __nfs_pageio_add_request(struct nfs_pageio_descriptor *desc, >> struct nfs_page *req) >> { >> - while (!nfs_pageio_do_add_request(desc, req)) { >> - desc->pg_moreio = 1; >> - nfs_pageio_doio(desc); >> - if (desc->pg_error < 0) >> - return 0; >> - desc->pg_moreio = 0; >> - if (desc->pg_recoalesce) >> - return 0; >> - } >> + struct nfs_page *subreq; >> + unsigned int bytes_left = 0; >> + unsigned int offset, pgbase; >> + >> + nfs_page_group_lock(req); >> + >> + subreq = req; >> + bytes_left = subreq->wb_bytes; >> + offset = subreq->wb_offset; >> + pgbase = subreq->wb_pgbase; >> + >> + do { >> + if (!nfs_pageio_do_add_request(desc, subreq)) { >> + /* make sure pg_test call(s) did nothing */ >> + WARN_ON_ONCE(subreq->wb_bytes != bytes_left); >> + WARN_ON_ONCE(subreq->wb_offset != offset); >> + WARN_ON_ONCE(subreq->wb_pgbase != pgbase); >> + >> + nfs_page_group_unlock(req); >> + desc->pg_moreio = 1; >> + nfs_pageio_doio(desc); >> + if (desc->pg_error < 0) >> + return 0; >> + desc->pg_moreio = 0; >> + if (desc->pg_recoalesce) >> + return 0; >> + /* retry add_request for this subreq */ >> + nfs_page_group_lock(req); >> + continue; >> + } >> + >> + /* check for buggy pg_test call(s) */ >> + WARN_ON_ONCE(subreq->wb_bytes + subreq->wb_pgbase > PAGE_SIZE); >> + WARN_ON_ONCE(subreq->wb_bytes > bytes_left); >> + WARN_ON_ONCE(subreq->wb_bytes == 0); >> + >> + bytes_left -= subreq->wb_bytes; >> + offset += subreq->wb_bytes; >> + pgbase += subreq->wb_bytes; >> + >> + if (bytes_left) { >> + subreq = nfs_create_request(req->wb_context, >> + req->wb_page, >> + subreq, pgbase, bytes_left); >> + nfs_lock_request(subreq); >> + subreq->wb_offset = offset; >> + subreq->wb_index = req->wb_index; >> + } >> + } while (bytes_left > 0); >> + >> + nfs_page_group_unlock(req); >> return 1; >> } >> >> diff --git a/fs/nfs/read.c b/fs/nfs/read.c >> index 95a0855..ee0a3cd 100644 >> --- a/fs/nfs/read.c >> +++ b/fs/nfs/read.c >> @@ -139,7 +139,7 @@ int nfs_readpage_async(struct nfs_open_context *ctx, struct inode *inode, >> len = nfs_page_length(page); >> if (len == 0) >> return nfs_return_empty_page(page); >> - new = nfs_create_request(ctx, page, 0, len); >> + new = nfs_create_request(ctx, page, NULL, 0, len); >> if (IS_ERR(new)) { >> unlock_page(page); >> return PTR_ERR(new); >> @@ -600,7 +600,7 @@ readpage_async_filler(void *data, struct page *page) >> if (len == 0) >> return nfs_return_empty_page(page); >> >> - new = nfs_create_request(desc->ctx, page, 0, len); >> + new = nfs_create_request(desc->ctx, page, NULL, 0, len); >> if (IS_ERR(new)) >> goto out_error; >> >> diff --git a/fs/nfs/write.c b/fs/nfs/write.c >> index ca20ec7..d1453f2 100644 >> --- a/fs/nfs/write.c >> +++ b/fs/nfs/write.c >> @@ -461,7 +461,7 @@ static void nfs_inode_remove_request(struct nfs_page *req) >> } >> nfsi->npages--; >> spin_unlock(&inode->i_lock); >> - nfs_release_request(req); >> + nfs_release_request(head); >> } >> >> static void >> @@ -625,6 +625,7 @@ static void nfs_write_completion(struct nfs_pgio_header *hdr) >> { >> struct nfs_commit_info cinfo; >> unsigned long bytes = 0; >> + bool do_destroy; >> >> if (test_bit(NFS_IOHDR_REDO, &hdr->flags)) >> goto out; >> @@ -654,6 +655,7 @@ remove_req: >> next: >> nfs_unlock_request(req); >> nfs_end_page_writeback(req->wb_page); >> + do_destroy = !test_bit(NFS_IOHDR_NEED_COMMIT, &hdr->flags); >> nfs_release_request(req); >> } >> out: >> @@ -758,6 +760,10 @@ static struct nfs_page *nfs_try_to_update_request(struct inode *inode, >> if (req == NULL) >> goto out_unlock; >> >> + /* should be handled by nfs_flush_incompatible */ >> + WARN_ON_ONCE(req->wb_head != req); >> + WARN_ON_ONCE(req->wb_this_page != req); >> + >> rqend = req->wb_offset + req->wb_bytes; >> /* >> * Tell the caller to flush out the request if >> @@ -819,7 +825,7 @@ static struct nfs_page * nfs_setup_write_request(struct nfs_open_context* ctx, >> req = nfs_try_to_update_request(inode, page, offset, bytes); >> if (req != NULL) >> goto out; >> - req = nfs_create_request(ctx, page, offset, bytes); >> + req = nfs_create_request(ctx, page, NULL, offset, bytes); >> if (IS_ERR(req)) >> goto out; >> nfs_inode_add_request(inode, req); >> @@ -863,6 +869,8 @@ int nfs_flush_incompatible(struct file *file, struct page *page) >> return 0; >> l_ctx = req->wb_lock_context; >> do_flush = req->wb_page != page || req->wb_context != ctx; >> + /* for now, flush if more than 1 request in page_group */ >> + do_flush |= req->wb_this_page != req; >> if (l_ctx && ctx->dentry->d_inode->i_flock != NULL) { >> do_flush |= l_ctx->lockowner.l_owner != current->files >> || l_ctx->lockowner.l_pid != current->tgid; >> diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h >> index 214e098..1fb161b 100644 >> --- a/include/linux/nfs_page.h >> +++ b/include/linux/nfs_page.h >> @@ -26,6 +26,8 @@ enum { >> PG_MAPPED, /* page private set for buffered io */ >> PG_CLEAN, /* write succeeded */ >> PG_COMMIT_TO_DS, /* used by pnfs layouts */ >> + PG_HEADLOCK, /* page group lock of wb_head */ >> + PG_TEARDOWN, /* page group sync for destroy */ >> }; >> >> struct nfs_inode; >> @@ -41,6 +43,8 @@ struct nfs_page { >> struct kref wb_kref; /* reference count */ >> unsigned long wb_flags; >> struct nfs_write_verifier wb_verf; /* Commit cookie */ >> + struct nfs_page *wb_this_page; /* list of reqs for this page */ >> + struct nfs_page *wb_head; /* head pointer for req list */ > > Hmm ok, so to make sure I understand... > > So page->private will point to the "head" req (struct page_private). Only in the buffered write case. Page->private is not set for read path / direct i/o path. > Then we'll have a singly-linked list of reqs hanging off of > wb_this_page. Is that right? > > If so, then it seems like it would be clearer to use a standard > list_head here. If you need to get to the wb_head, you could always do > something like this: > > list_first_entry(&req->wb_page->wb_this_page); Well, wb_page is a struct page and doesn?t have wb_this_page (which is in struct nfs_page), but I see where you?re going with this. A strategy like this only works if we always have page->private pointing to the head request. We chose not to go that way because it messes with the buffered write path?s setting / clearing of page private which interacts with the swappable nfs pages code that everyone seems to be afraid to touch ;) So we decided to go this route (not messing with page_private) as a first step - we certainly could add it later, but the current approach makes things less complex. > > ...and could even turn that into a macro or static inline for some > syntactic sugar. It's a little more pointer chasing to find the head, > but it seems like that would be clearer than using yet another > linked-list implementation. So, I?m not against using list_head.. I didn?t go that route initially because I was: 1) following the buffer_head example, which rolls it?s own list 2) trying to grow nfs_page as little as possible - but we might have room within the allocator bucket it currently lives in? 3) not sure list_head is suitable for a circular list (I haven?t ever looked into it). and until we have a way to find the head request (via page private, etc) without walking the circular list (chicken / egg problem needing to grab head lock before walking list to find the head to lock it), we?ll still need the head pointer. Thoughts? -dros > >> }; >> >> struct nfs_pageio_descriptor; >> @@ -75,9 +79,10 @@ struct nfs_pageio_descriptor { >> >> extern struct nfs_page *nfs_create_request(struct nfs_open_context *ctx, >> struct page *page, >> + struct nfs_page *last, >> unsigned int offset, >> unsigned int count); >> -extern void nfs_release_request(struct nfs_page *req); >> +extern void nfs_release_request(struct nfs_page *); >> >> >> extern void nfs_pageio_init(struct nfs_pageio_descriptor *desc, >> @@ -95,7 +100,10 @@ extern size_t nfs_generic_pg_test(struct nfs_pageio_descriptor *desc, >> struct nfs_page *req); >> extern int nfs_wait_on_request(struct nfs_page *); >> extern void nfs_unlock_request(struct nfs_page *req); >> -extern void nfs_unlock_and_release_request(struct nfs_page *req); >> +extern void nfs_unlock_and_release_request(struct nfs_page *); >> +extern void nfs_page_group_lock(struct nfs_page *); >> +extern void nfs_page_group_unlock(struct nfs_page *); >> +extern bool nfs_page_group_sync_on_bit(struct nfs_page *, unsigned int); >> >> /* >> * Lock the page of an asynchronous request > > > -- > Jeff Layton