On Apr 24, 2014, at 11:45 AM, Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote:
> On Thu, 24 Apr 2014 11:23:19 -0400
> Weston Andros Adamson <dros@xxxxxxxxxxxxxxx> wrote:
>
>> On Apr 24, 2014, at 10:50 AM, Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote:
>>
>>> On Tue, 22 Apr 2014 17:29:13 -0400
>>> Weston Andros Adamson <dros@xxxxxxxxxxxxxxx> 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 <dros@xxxxxxxxxxxxxxx>
>>>> ---
>>>> 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.
>>
>
> Doh, right! Sorry, I threw that together in haste, but you get the
> idea. I was thinking you could go back to the page and dereference
> ->private.
>
>> 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.
>>
>
> Ok, that makes sense. Thanks...
>
>>>
>>> ...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
>>
>
> I wouldn't be surprised if the buffer_head code predates the standard
> linked-list macros, so that probably explains why they did it that way.
> The file locking code has a similar construct in inode->i_flock list.
AFAIK the sub-page functionality was added somewhat recently.
>
>> 2) trying to grow nfs_page as little as possible - but we might have room within
>> the allocator bucket it currently lives in…
>>
>
> nfs_page comes out of a dedicated slabcache, so that probably won't be the case.
Ah, right!
>
>> 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
>>
>
> If you can't rely on page->private pointing to the request, then that
> does make it tough to do what I was suggesting. struct list_head lists
> are doubly-linked and circular by nature, so that does seem to be a
> natural fit for what you're trying to do.
Oh I see -- you’re totally right about list_head being circular, one just has
to call for_each on whatever head they wish to start from.
>
> The only problem is that struct list_head is two pointers instead of
> one, so it's not going to be as space-efficient as what you're doing
> here. If that's a large concern then you may have no choice but to do
> this after all.
Right. How much do we care about an extra pointer here? It seems to me
that we should try to keep it as small as possible - I know Trond has been unwilling
to add members to rpc_task (for example) unless absolutely necessary and there will
be at least one (if not more) nfs_page structures per rpc_task.
One immediate takeaway: I need to add much better comments about this.
As far as eventually removing the wb_head pointer, it gets really ugly to do without
changing the buffered write path (and swappable page semantics) because page_group
operations happen *after* nfs_inode_remove_request() clears page_private (syncing the
destruction of the page group). This means that nfs_release_request and
nfs_unlock_and_release_request will both have to be passed a previously cached head
pointer. yuck.
-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 <jlayton@xxxxxxxxxxxxxxx>
>>
>
>
> --
> Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
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