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Re: [PATCH] 9pfs: use GHashMap for fid table
From: |
Christian Schoenebeck |
Subject: |
Re: [PATCH] 9pfs: use GHashMap for fid table |
Date: |
Sun, 04 Sep 2022 20:06:57 +0200 |
On Samstag, 3. September 2022 17:03:27 CEST Linus Heckemann wrote:
> The previous implementation would iterate over the fid table for
> lookup operations, resulting in an operation with O(n) complexity on
> the number of open files and poor cache locality -- for nearly every
> open, stat, read, write, etc operation.
Oh yes, I had this on my TODO list for a long time. Thanks for the effort
Linus!
> This change uses a hashtable for this instead, significantly improving
> the performance of the 9p filesystem. The runtime of NixOS's simple
> installer test, which copies ~122k files totalling ~1.8GiB from 9p,
> decreased by a factor of about 10.
Wow, even more than I expected. Nice!
I have a feeling that this will also fix the massive slow downs that were seen
after running for a long time. Because I think that slow down was because a
large amount of fids were accumulated over time, where this O(n) issue hurts
more noticably.
Some remarks below ...
> Signed-off-by: Linus Heckemann <git@sphalerite.org>
> ---
> hw/9pfs/9p.c | 130 +++++++++++++++++++++++++++------------------------
> hw/9pfs/9p.h | 2 +-
> 2 files changed, 69 insertions(+), 63 deletions(-)
>
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index aebadeaa03..ff466afe39 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -282,33 +282,31 @@ static V9fsFidState *coroutine_fn get_fid(V9fsPDU
> *pdu, int32_t fid) V9fsFidState *f;
> V9fsState *s = pdu->s;
>
> - QSIMPLEQ_FOREACH(f, &s->fid_list, next) {
> - BUG_ON(f->clunked);
> - if (f->fid == fid) {
> - /*
> - * Update the fid ref upfront so that
> - * we don't get reclaimed when we yield
> - * in open later.
> - */
> - f->ref++;
> - /*
> - * check whether we need to reopen the
> - * file. We might have closed the fd
> - * while trying to free up some file
> - * descriptors.
> - */
> - err = v9fs_reopen_fid(pdu, f);
> - if (err < 0) {
> - f->ref--;
> - return NULL;
> - }
> - /*
> - * Mark the fid as referenced so that the LRU
> - * reclaim won't close the file descriptor
> - */
> - f->flags |= FID_REFERENCED;
> - return f;
> + f = g_hash_table_lookup(s->fids, GINT_TO_POINTER(fid));
> + if (f) {
> + /*
> + * Update the fid ref upfront so that
> + * we don't get reclaimed when we yield
> + * in open later.
> + */
> + f->ref++;
> + /*
> + * check whether we need to reopen the
> + * file. We might have closed the fd
> + * while trying to free up some file
> + * descriptors.
> + */
> + err = v9fs_reopen_fid(pdu, f);
> + if (err < 0) {
> + f->ref--;
> + return NULL;
> }
> + /*
> + * Mark the fid as referenced so that the LRU
> + * reclaim won't close the file descriptor
> + */
> + f->flags |= FID_REFERENCED;
> + return f;
> }
> return NULL;
> }
> @@ -317,12 +315,9 @@ static V9fsFidState *alloc_fid(V9fsState *s, int32_t
> fid) {
> V9fsFidState *f;
>
> - QSIMPLEQ_FOREACH(f, &s->fid_list, next) {
> + if (g_hash_table_contains(s->fids, GINT_TO_POINTER(fid))) {
> /* If fid is already there return NULL */
> - BUG_ON(f->clunked);
> - if (f->fid == fid) {
> - return NULL;
> - }
> + return NULL;
Probably retaining BUG_ON(f->clunked) here?
> }
> f = g_new0(V9fsFidState, 1);
> f->fid = fid;
> @@ -333,7 +328,7 @@ static V9fsFidState *alloc_fid(V9fsState *s, int32_t
> fid) * reclaim won't close the file descriptor
> */
> f->flags |= FID_REFERENCED;
> - QSIMPLEQ_INSERT_TAIL(&s->fid_list, f, next);
> + g_hash_table_insert(s->fids, GINT_TO_POINTER(fid), f);
>
> v9fs_readdir_init(s->proto_version, &f->fs.dir);
> v9fs_readdir_init(s->proto_version, &f->fs_reclaim.dir);
> @@ -424,12 +419,11 @@ static V9fsFidState *clunk_fid(V9fsState *s, int32_t
> fid) {
> V9fsFidState *fidp;
>
> - QSIMPLEQ_FOREACH(fidp, &s->fid_list, next) {
> - if (fidp->fid == fid) {
> - QSIMPLEQ_REMOVE(&s->fid_list, fidp, V9fsFidState, next);
> - fidp->clunked = true;
> - return fidp;
> - }
> + fidp = g_hash_table_lookup(s->fids, GINT_TO_POINTER(fid));
> + if (fidp) {
> + g_hash_table_remove(s->fids, GINT_TO_POINTER(fid));
> + fidp->clunked = true;
> + return fidp;
We can't get rid of the double lookup here, can we? Surprisingly I don't find
a lookup function on the iterator based API.
> }
> return NULL;
> }
> @@ -439,10 +433,15 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu)
> int reclaim_count = 0;
> V9fsState *s = pdu->s;
> V9fsFidState *f;
> +
> + GHashTableIter iter;
> + gpointer fid;
> + g_hash_table_iter_init(&iter, s->fids);
> +
> QSLIST_HEAD(, V9fsFidState) reclaim_list =
> QSLIST_HEAD_INITIALIZER(reclaim_list);
>
> - QSIMPLEQ_FOREACH(f, &s->fid_list, next) {
> + while (g_hash_table_iter_next(&iter, &fid, (void **) &f)) {
> /*
> * Unlink fids cannot be reclaimed. Check
> * for them and skip them. Also skip fids
> @@ -518,12 +517,12 @@ static int coroutine_fn
> v9fs_mark_fids_unreclaim(V9fsPDU *pdu, V9fsPath *path) {
> int err;
> V9fsState *s = pdu->s;
> - V9fsFidState *fidp, *fidp_next;
> + V9fsFidState *fidp;
> + gpointer fid;
> +
> + GHashTableIter iter;
> + g_hash_table_iter_init(&iter, s->fids);
>
> - fidp = QSIMPLEQ_FIRST(&s->fid_list);
> - if (!fidp) {
> - return 0;
> - }
>
> /*
> * v9fs_reopen_fid() can yield : a reference on the fid must be held
> @@ -534,7 +533,13 @@ static int coroutine_fn
> v9fs_mark_fids_unreclaim(V9fsPDU *pdu, V9fsPath *path) * iteration after we
> could get a reference on the next fid. Start with * the first one.
> */
> - for (fidp->ref++; fidp; fidp = fidp_next) {
> + while (g_hash_table_iter_next(&iter, &fid, (void **) &fidp)) {
Too bad that there's apparently no macro based g_hash_table_foreach(), that
would have made the code a bit cleaner and shorter than using an iterator
while loop, but OK.
Best regards,
Christian Schoenebeck
> + /*
> + * Ensure the fid survives a potential clunk request during
> + * put_fid() below and v9fs_reopen_fid() in the next iteration.
> + */
> + fidp->ref++;
> +
> if (fidp->path.size == path->size &&
> !memcmp(fidp->path.data, path->data, path->size)) {
> /* Mark the fid non reclaimable. */
> @@ -548,16 +553,6 @@ static int coroutine_fn
> v9fs_mark_fids_unreclaim(V9fsPDU *pdu, V9fsPath *path) }
> }
>
> - fidp_next = QSIMPLEQ_NEXT(fidp, next);
> -
> - if (fidp_next) {
> - /*
> - * Ensure the next fid survives a potential clunk request
> during - * put_fid() below and v9fs_reopen_fid() in the next
> iteration. - */
> - fidp_next->ref++;
> - }
> -
> /* We're done with this fid */
> put_fid(pdu, fidp);
> }
> @@ -570,18 +565,20 @@ static void coroutine_fn virtfs_reset(V9fsPDU *pdu)
> V9fsState *s = pdu->s;
> V9fsFidState *fidp;
>
> + gpointer fid;
> + GHashTableIter iter;
> + g_hash_table_iter_init(&iter, s->fids);
> +
> /* Free all fids */
> - while (!QSIMPLEQ_EMPTY(&s->fid_list)) {
> - /* Get fid */
> - fidp = QSIMPLEQ_FIRST(&s->fid_list);
> + while (g_hash_table_iter_next(&iter, &fid, (void **) &fidp)) {
> fidp->ref++;
>
> /* Clunk fid */
> - QSIMPLEQ_REMOVE(&s->fid_list, fidp, V9fsFidState, next);
> fidp->clunked = true;
>
> put_fid(pdu, fidp);
> }
> + g_hash_table_remove_all(s->fids);
> }
>
> #define P9_QID_TYPE_DIR 0x80
> @@ -3206,6 +3203,9 @@ static int coroutine_fn v9fs_complete_rename(V9fsPDU
> *pdu, V9fsFidState *fidp, V9fsState *s = pdu->s;
> V9fsFidState *dirfidp = NULL;
>
> + GHashTableIter iter;
> + gpointer fid;
> +
> v9fs_path_init(&new_path);
> if (newdirfid != -1) {
> dirfidp = get_fid(pdu, newdirfid);
> @@ -3238,11 +3238,13 @@ static int coroutine_fn v9fs_complete_rename(V9fsPDU
> *pdu, V9fsFidState *fidp, if (err < 0) {
> goto out;
> }
> +
> /*
> * Fixup fid's pointing to the old name to
> * start pointing to the new name
> */
> - QSIMPLEQ_FOREACH(tfidp, &s->fid_list, next) {
> + g_hash_table_iter_init(&iter, s->fids);
> + while (g_hash_table_iter_next(&iter, &fid, (void **) &tfidp)) {
> if (v9fs_path_is_ancestor(&fidp->path, &tfidp->path)) {
> /* replace the name */
> v9fs_fix_path(&tfidp->path, &new_path,
> strlen(fidp->path.data)); @@ -3321,6 +3323,9 @@ static int coroutine_fn
> v9fs_fix_fid_paths(V9fsPDU *pdu, V9fsPath *olddir, V9fsState *s = pdu->s;
> int err;
>
> + GHashTableIter iter;
> + gpointer fid;
> +
> v9fs_path_init(&oldpath);
> v9fs_path_init(&newpath);
> err = v9fs_co_name_to_path(pdu, olddir, old_name->data, &oldpath);
> @@ -3336,7 +3341,8 @@ static int coroutine_fn v9fs_fix_fid_paths(V9fsPDU
> *pdu, V9fsPath *olddir, * Fixup fid's pointing to the old name to
> * start pointing to the new name
> */
> - QSIMPLEQ_FOREACH(tfidp, &s->fid_list, next) {
> + g_hash_table_iter_init(&iter, s->fids);
> + while (g_hash_table_iter_next(&iter, &fid, (void **) &tfidp)) {
> if (v9fs_path_is_ancestor(&oldpath, &tfidp->path)) {
> /* replace the name */
> v9fs_fix_path(&tfidp->path, &newpath, strlen(oldpath.data));
> @@ -4226,7 +4232,7 @@ int v9fs_device_realize_common(V9fsState *s, const
> V9fsTransport *t, s->ctx.fmode = fse->fmode;
> s->ctx.dmode = fse->dmode;
>
> - QSIMPLEQ_INIT(&s->fid_list);
> + s->fids = g_hash_table_new(NULL, NULL);
> qemu_co_rwlock_init(&s->rename_lock);
>
> if (s->ops->init(&s->ctx, errp) < 0) {
> diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
> index 994f952600..10fd2076c2 100644
> --- a/hw/9pfs/9p.h
> +++ b/hw/9pfs/9p.h
> @@ -339,7 +339,7 @@ typedef struct {
> struct V9fsState {
> QLIST_HEAD(, V9fsPDU) free_list;
> QLIST_HEAD(, V9fsPDU) active_list;
> - QSIMPLEQ_HEAD(, V9fsFidState) fid_list;
> + GHashTable *fids;
> FileOperations *ops;
> FsContext ctx;
> char *tag;