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Re: [PATCH v3] 9pfs: use GHashTable for fid table
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From: |
Greg Kurz |
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Subject: |
Re: [PATCH v3] 9pfs: use GHashTable for fid table |
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Date: |
Thu, 8 Sep 2022 14:18:41 +0200 |
On Thu, 8 Sep 2022 13:23:53 +0200
Linus Heckemann <git@sphalerite.org> 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 every open,
> stat, read, write, etc operation.
>
> 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.
>
> Signed-off-by: Linus Heckemann <git@sphalerite.org>
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> Reviewed-by: Greg Kurz <groug@kaod.org>
> ---
>
> Greg Kurz writes:
> > The comment above should be adapted to the new situation : no need
>
> I've removed it completely, since the logic is simple enough that only
> the shortened comment below remains necessary.
>
> > With the new logic, this should just be:
>
> now is :)
>
> > g_hash_table_steal_extended() [1] actually allows to do just that.
>
> g_hash_table_steal_extended unfortunately isn't available since it was
> introduced in glib 2.58 and we're maintaining compatibility to 2.56.
>
Ha... this could be addressed through conditional compilation, e.g.:
static V9fsFidState *clunk_fid(V9fsState *s, int32_t fid)
{
V9fsFidState *fidp;
#if GLIB_CHECK_VERSION(2,56,0)
if (!g_hash_table_steal_extended(s->fids, GINT_TO_POINTER(fid),
NULL, (gpointer *) &fidp)) {
return NULL;
}
#else
fidp = g_hash_table_lookup(s->fids, GINT_TO_POINTER(fid));
if (fidp) {
g_hash_table_remove(s->fids, GINT_TO_POINTER(fid));
} else {
return NULL;
}
#endif
fidp->clunked = true;
return fidp;
}
or simply leave a TODO comment so that we don't forget.
> > You could just call g_hash_table_iter_remove(&iter) here
>
> Applied this suggestion, thanks!
>
>
> > Well... finding at least one clunked fid state in this table is
> > definitely a bug so I'll keep the BUG_ON() anyway.
>
> Christian Schoenebeck writes:
> > Yeah, I think you are right, it would feel odd. Just drop BUG_ON() for
> > now.
>
> I still prefer dropping it, but if we were to keep it I think it should
> be in v9fs_reclaim_fd where we iterate and can thus check the whole
> table.
>
IMO the relevant aspect isn't really about checking the whole table, but
rather not to get a clunked fid out of this table and pass it over.
>
> Greg Kurz and Philippe Mathieu-Daudé write:
> > [patch versioning]
>
> Whoops. I used -v2 on git send-email, which just ignored the option,
> rather than git format-patch, by accident. This one _should_ now be v3!
>
>
v3 it is and LGTM ! No big deal with the BUG_ON(), given the improvement.
My R-b stands. Thanks Linus !
> hw/9pfs/9p.c | 140 +++++++++++++++++++++++++--------------------------
> hw/9pfs/9p.h | 2 +-
> 2 files changed, 70 insertions(+), 72 deletions(-)
>
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index aebadeaa03..98a475e560 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;
> }
> 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;
> }
> 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, (gpointer *) &f)) {
> /*
> * Unlink fids cannot be reclaimed. Check
> * for them and skip them. Also skip fids
> @@ -518,23 +517,19 @@ 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;
>
> - fidp = QSIMPLEQ_FIRST(&s->fid_list);
> - if (!fidp) {
> - return 0;
> - }
> + g_hash_table_iter_init(&iter, s->fids);
> +
> + while (g_hash_table_iter_next(&iter, &fid, (gpointer *) &fidp)) {
> + /*
> + * Ensure the fid survives a potential clunk request during
> + * v9fs_reopen_fid.
> + */
> + fidp->ref++;
>
> - /*
> - * v9fs_reopen_fid() can yield : a reference on the fid must be held
> - * to ensure its pointer remains valid and we can safely pass it to
> - * QSIMPLEQ_NEXT(). The corresponding put_fid() can also yield so
> - * we must keep a reference on the next fid as well. So the logic here
> - * is to get a reference on a fid and only put it back during the next
> - * iteration after we could get a reference on the next fid. Start with
> - * the first one.
> - */
> - for (fidp->ref++; fidp; fidp = fidp_next) {
> if (fidp->path.size == path->size &&
> !memcmp(fidp->path.data, path->data, path->size)) {
> /* Mark the fid non reclaimable. */
> @@ -548,16 +543,6 @@ 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);
> }
> @@ -569,18 +554,20 @@ 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, (gpointer *) &fidp)) {
> fidp->ref++;
>
> /* Clunk fid */
> - QSIMPLEQ_REMOVE(&s->fid_list, fidp, V9fsFidState, next);
> fidp->clunked = true;
>
> put_fid(pdu, fidp);
> + g_hash_table_iter_remove(&iter);
> }
> }
>
> @@ -3205,6 +3192,8 @@ static int coroutine_fn v9fs_complete_rename(V9fsPDU
> *pdu, V9fsFidState *fidp,
> V9fsFidState *tfidp;
> V9fsState *s = pdu->s;
> V9fsFidState *dirfidp = NULL;
> + GHashTableIter iter;
> + gpointer fid;
>
> v9fs_path_init(&new_path);
> if (newdirfid != -1) {
> @@ -3238,11 +3227,13 @@ 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, (gpointer *) &tfidp)) {
> if (v9fs_path_is_ancestor(&fidp->path, &tfidp->path)) {
> /* replace the name */
> v9fs_fix_path(&tfidp->path, &new_path, strlen(fidp->path.data));
> @@ -3320,6 +3311,8 @@ static int coroutine_fn v9fs_fix_fid_paths(V9fsPDU
> *pdu, V9fsPath *olddir,
> V9fsPath oldpath, newpath;
> V9fsState *s = pdu->s;
> int err;
> + GHashTableIter iter;
> + gpointer fid;
>
> v9fs_path_init(&oldpath);
> v9fs_path_init(&newpath);
> @@ -3336,7 +3329,8 @@ 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, (gpointer *) &tfidp)) {
> if (v9fs_path_is_ancestor(&oldpath, &tfidp->path)) {
> /* replace the name */
> v9fs_fix_path(&tfidp->path, &newpath, strlen(oldpath.data));
> @@ -4226,7 +4220,7 @@ 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) {
> @@ -4286,6 +4280,10 @@ void v9fs_device_unrealize_common(V9fsState *s)
> if (s->ctx.fst) {
> fsdev_throttle_cleanup(s->ctx.fst);
> }
> + if (s->fids) {
> + g_hash_table_destroy(s->fids);
> + s->fids = NULL;
> + }
> g_free(s->tag);
> qp_table_destroy(&s->qpd_table);
> qp_table_destroy(&s->qpp_table);
> 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;