| Message ID | 20230907033914epcms1p61c5eed4d34d5c4212436c201f33292b3@epcms1p6 (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | maple_tree: use GFP_KERNEL on mas_node_count | expand |
On Thu, Sep 07, 2023 at 12:39:14PM +0900, 심재선 wrote: > Use GFP_KERNEL on mas_node_count instead of GFP_NOWAIT | __GFP_NOWARN > in order to allow memory reclaim. What testing did you do of this patch? In particular, did you try it with lockdep enabled?
在 2023/9/7 11:49, Matthew Wilcox 写道: > On Thu, Sep 07, 2023 at 12:39:14PM +0900, 심재선 wrote: >> Use GFP_KERNEL on mas_node_count instead of GFP_NOWAIT | __GFP_NOWARN >> in order to allow memory reclaim. There are many paths that call maple tree's mas_node_count(). Some paths cannot reclaim memory. > > What testing did you do of this patch? In particular, did you try it > with lockdep enabled? >
On Thu, Sep 07, 2023 at 12:02:02PM +0800, Peng Zhang wrote: > > > 在 2023/9/7 11:49, Matthew Wilcox 写道: > > On Thu, Sep 07, 2023 at 12:39:14PM +0900, 심재선 wrote: > > > Use GFP_KERNEL on mas_node_count instead of GFP_NOWAIT | __GFP_NOWARN > > > in order to allow memory reclaim. > There are many paths that call maple tree's mas_node_count(). Some paths > cannot reclaim memory. Right ... but we should be handling the ENOMEM inside the maple tree and allocating some nodes with GFP_KERNEL instead of failing fork(). > > What testing did you do of this patch? In particular, did you try it > > with lockdep enabled?
> On Thu, Sep 07, 2023 at 12:02:02PM +0800, Peng Zhang wrote: > > > > > > 在 2023/9/7 11:49, Matthew Wilcox 写道: > > > On Thu, Sep 07, 2023 at 12:39:14PM +0900, 심재선 wrote: > > > > Use GFP_KERNEL on mas_node_count instead of GFP_NOWAIT | __GFP_NOWARN > > > > in order to allow memory reclaim. > > There are many paths that call maple tree's mas_node_count(). Some paths > > cannot reclaim memory. > > Right ... but we should be handling the ENOMEM inside the maple tree and > allocating some nodes with GFP_KERNEL instead of failing fork(). > > > > What testing did you do of this patch? In particular, did you try it > > > with lockdep enabled? I did power on/off test with this patch. I did not try it with lockdep enabled.
* Jaeseon Sim <jason.sim@samsung.com> [230907 00:41]: > > On Thu, Sep 07, 2023 at 12:02:02PM +0800, Peng Zhang wrote: > > > > > > > > > 在 2023/9/7 11:49, Matthew Wilcox 写道: > > > > On Thu, Sep 07, 2023 at 12:39:14PM +0900, 심재선 wrote: > > > > > Use GFP_KERNEL on mas_node_count instead of GFP_NOWAIT | __GFP_NOWARN > > > > > in order to allow memory reclaim. > > > There are many paths that call maple tree's mas_node_count(). Some paths > > > cannot reclaim memory. > > > > Right ... but we should be handling the ENOMEM inside the maple tree and > > allocating some nodes with GFP_KERNEL instead of failing fork(). > > > > > > What testing did you do of this patch? In particular, did you try it > > > > with lockdep enabled? > I did power on/off test with this patch. > I did not try it with lockdep enabled. To accomplish the same result, but with a much smaller scope that will work with lockdep, I would suggest changing mas_expected_entries() to use mas_node_count_gfp() (which already exists) and pass in GFP_KERNEL. Since fork is the only current user of mas_expected_entries(), this won't break other users and we can deal with changing it for others if it is needed. If we do go this route, please add a note in the documentation about using GFP_KERNEL. Willy, does that work for you? Thanks, Liam
> * Jaeseon Sim <jason.sim@samsung.com> [230907 00:41]: > > > On Thu, Sep 07, 2023 at 12:02:02PM +0800, Peng Zhang wrote: > > > > > > > > > > > > 在 2023/9/7 11:49, Matthew Wilcox 写道: > > > > > On Thu, Sep 07, 2023 at 12:39:14PM +0900, 심재선 wrote: > > > > > > Use GFP_KERNEL on mas_node_count instead of GFP_NOWAIT | __GFP_NOWARN > > > > > > in order to allow memory reclaim. > > > > There are many paths that call maple tree's mas_node_count(). Some paths > > > > cannot reclaim memory. > > > > > > Right ... but we should be handling the ENOMEM inside the maple tree and > > > allocating some nodes with GFP_KERNEL instead of failing fork(). > > > > > > > > What testing did you do of this patch? In particular, did you try it > > > > > with lockdep enabled? > > I did power on/off test with this patch. > > I did not try it with lockdep enabled. > > To accomplish the same result, but with a much smaller scope that will > work with lockdep, I would suggest changing mas_expected_entries() to > use mas_node_count_gfp() (which already exists) and pass in GFP_KERNEL. > > Since fork is the only current user of mas_expected_entries(), this > won't break other users and we can deal with changing it for others if > it is needed. > > If we do go this route, please add a note in the documentation about > using GFP_KERNEL. > > Willy, does that work for you? > > Thanks, > Liam Dear Liam, Can I ask you the reason why mas_node_count is using GFP_NOWAIT | __GFP_NOWARN? I wonder if other callers for mas_node_count might have similar issue. From your opinion, I'll post v2 patch as follows diff --git a/lib/maple_tree.c b/lib/maple_tree.c index ee1ff0c59fd7..b0229271c24e 100644 --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -5574,7 +5574,7 @@ int mas_expected_entries(struct ma_state *mas, unsigned long nr_entries) /* Internal nodes */ nr_nodes += DIV_ROUND_UP(nr_nodes, nonleaf_cap); /* Add working room for split (2 nodes) + new parents */ - mas_node_count(mas, nr_nodes + 3); + mas_node_count_gfp(mas, nr_nodes + 3, GFP_KERNEL); /* Detect if allocations run out */ mas->mas_flags |= MA_STATE_PREALLOC;
* Jaeseon Sim <jason.sim@samsung.com> [230913 22:49]: > > * Jaeseon Sim <jason.sim@samsung.com> [230907 00:41]: > > > > On Thu, Sep 07, 2023 at 12:02:02PM +0800, Peng Zhang wrote: > > > > > > > > > > > > > > > 在 2023/9/7 11:49, Matthew Wilcox 写道: > > > > > > On Thu, Sep 07, 2023 at 12:39:14PM +0900, 심재선 wrote: > > > > > > > Use GFP_KERNEL on mas_node_count instead of GFP_NOWAIT | __GFP_NOWARN > > > > > > > in order to allow memory reclaim. > > > > > There are many paths that call maple tree's mas_node_count(). Some paths > > > > > cannot reclaim memory. > > > > > > > > Right ... but we should be handling the ENOMEM inside the maple tree and > > > > allocating some nodes with GFP_KERNEL instead of failing fork(). > > > > > > > > > > What testing did you do of this patch? In particular, did you try it > > > > > > with lockdep enabled? > > > I did power on/off test with this patch. > > > I did not try it with lockdep enabled. > > > > To accomplish the same result, but with a much smaller scope that will > > work with lockdep, I would suggest changing mas_expected_entries() to > > use mas_node_count_gfp() (which already exists) and pass in GFP_KERNEL. > > > > Since fork is the only current user of mas_expected_entries(), this > > won't break other users and we can deal with changing it for others if > > it is needed. > > > > If we do go this route, please add a note in the documentation about > > using GFP_KERNEL. > > > > Willy, does that work for you? > > > > Thanks, > > Liam > > Dear Liam, > Can I ask you the reason why mas_node_count is using GFP_NOWAIT | __GFP_NOWARN? Must users in the VMA space have complicated locking schemes which require no sleeping during a store operation. Most operations will drop the lock and re-try with GFP_KERNEL when using the internal lock (see mas_nomem()). > I wonder if other callers for mas_node_count might have similar issue. The external callers who need GFP_KERNEL are either using mas_store_gfp() or mas_prealloc to set up a store prior to taking a series of other locks. During a mas_prealloc() or mas_expected_entries() call, we set the MA_STATE_PREALLOC flag to indicate that there are nodes preallocated. This is to catch users who call mas_node_count() and require increased allocations when allocations should not be taken. You can see this flag directly below the line you modified. > > From your opinion, I'll post v2 patch as follows Thanks. Please test with lockdep but I don't see a nesting lock issue with fork and this change. > > diff --git a/lib/maple_tree.c b/lib/maple_tree.c > index ee1ff0c59fd7..b0229271c24e 100644 > --- a/lib/maple_tree.c > +++ b/lib/maple_tree.c > @@ -5574,7 +5574,7 @@ int mas_expected_entries(struct ma_state *mas, unsigned long nr_entries) > /* Internal nodes */ > nr_nodes += DIV_ROUND_UP(nr_nodes, nonleaf_cap); > /* Add working room for split (2 nodes) + new parents */ > - mas_node_count(mas, nr_nodes + 3); > + mas_node_count_gfp(mas, nr_nodes + 3, GFP_KERNEL); > > /* Detect if allocations run out */ > mas->mas_flags |= MA_STATE_PREALLOC; > -- > 2.17.1 > > Thanks > Jaeseon
diff --git a/lib/maple_tree.c b/lib/maple_tree.c index ee1ff0c59fd7..076798f83baa 100644 --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -1336,11 +1336,11 @@ static void mas_node_count_gfp(struct ma_state *mas, int count, gfp_t gfp) * @mas: The maple state * @count: The number of nodes needed * - * Note: Uses GFP_NOWAIT | __GFP_NOWARN for gfp flags. + * Note: Uses GFP_KERNEL for gfp flags. */ static void mas_node_count(struct ma_state *mas, int count) { - return mas_node_count_gfp(mas, count, GFP_NOWAIT | __GFP_NOWARN); + return mas_node_count_gfp(mas, count, GFP_KERNEL); } /*
Use GFP_KERNEL on mas_node_count instead of GFP_NOWAIT | __GFP_NOWARN in order to allow memory reclaim. Currently, fork errors occur on low free memory as follows: Zygote : Failed to fork child process: Out of memory (12) -ENOMEM was returned as following path: mas_node_count mas_expected_entries dup_mmap dup_mm copy_mm copy_process Signed-off-by: jason.sim <jason.sim@samsung.com> --- lib/maple_tree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)