| Message ID | 20230109051823.480289-3-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Remove AS_EIO and AS_ENOSPC | expand |
On Mon, 2023-01-09 at 05:18 +0000, Matthew Wilcox (Oracle) wrote: > Convert both callers to use the "new" errseq infrastructure. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > mm/filemap.c | 18 ++++++------------ > 1 file changed, 6 insertions(+), 12 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index c4d4ace9cc70..48daedc224d9 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -355,16 +355,6 @@ int filemap_check_errors(struct address_space *mapping) > } > EXPORT_SYMBOL(filemap_check_errors); > > -static int filemap_check_and_keep_errors(struct address_space *mapping) > -{ > - /* Check for outstanding write errors */ > - if (test_bit(AS_EIO, &mapping->flags)) > - return -EIO; > - if (test_bit(AS_ENOSPC, &mapping->flags)) > - return -ENOSPC; > - return 0; > -} > - > /** > * filemap_fdatawrite_wbc - start writeback on mapping dirty pages in range > * @mapping: address space structure to write > @@ -567,8 +557,10 @@ EXPORT_SYMBOL(filemap_fdatawait_range); > int filemap_fdatawait_range_keep_errors(struct address_space *mapping, > loff_t start_byte, loff_t end_byte) > { > + errseq_t since = filemap_sample_wb_err(mapping); > + > __filemap_fdatawait_range(mapping, start_byte, end_byte); > - return filemap_check_and_keep_errors(mapping); > + return filemap_check_wb_err(mapping, since); > } > EXPORT_SYMBOL(filemap_fdatawait_range_keep_errors); I looked at making this sort of change across the board alongside the original wb_err patches, but I backed off at the time. With the above patch, this function will no longer report a writeback error that occurs before the sample. Given that writeback can happen at any time, that seemed like it might be an undesirable change, and I didn't follow through. It is true that the existing flag-based code may miss errors too, if multiple tasks are test_and_clear'ing the bits, but I think the above is even more likely to happen, esp. under memory pressure. To do this right, we probably need to look at these callers and have them track a long-term errseq_t "since" value before they ever dirty the pages, and then continually check-and-advance vs. that. For instance, the main caller of the above function is jbd2. Would it be reasonable to add in a new errseq_t value to the jnode for tracking errors? > > @@ -613,8 +605,10 @@ EXPORT_SYMBOL(file_fdatawait_range); > */ > int filemap_fdatawait_keep_errors(struct address_space *mapping) > { > + errseq_t since = filemap_sample_wb_err(mapping); > + > __filemap_fdatawait_range(mapping, 0, LLONG_MAX); > - return filemap_check_and_keep_errors(mapping); > + return filemap_check_wb_err(mapping, since); > } > EXPORT_SYMBOL(filemap_fdatawait_keep_errors); >
On Mon, Jan 09, 2023 at 08:48:49AM -0500, Jeff Layton wrote: > On Mon, 2023-01-09 at 05:18 +0000, Matthew Wilcox (Oracle) wrote: > > Convert both callers to use the "new" errseq infrastructure. > > I looked at making this sort of change across the board alongside the > original wb_err patches, but I backed off at the time. > > With the above patch, this function will no longer report a writeback > error that occurs before the sample. Given that writeback can happen at > any time, that seemed like it might be an undesirable change, and I > didn't follow through. > > It is true that the existing flag-based code may miss errors too, if > multiple tasks are test_and_clear'ing the bits, but I think the above is > even more likely to happen, esp. under memory pressure. > > To do this right, we probably need to look at these callers and have > them track a long-term errseq_t "since" value before they ever dirty the > pages, and then continually check-and-advance vs. that. > > For instance, the main caller of the above function is jbd2. Would it be > reasonable to add in a new errseq_t value to the jnode for tracking > errors? Doesn't b4678df184b3 address this problem? If nobody has seen the error, we return 0 instead of the current value of wb_err, ensuring that somebody always sees the error.
On Mon, 2023-01-09 at 14:02 +0000, Matthew Wilcox wrote: > On Mon, Jan 09, 2023 at 08:48:49AM -0500, Jeff Layton wrote: > > On Mon, 2023-01-09 at 05:18 +0000, Matthew Wilcox (Oracle) wrote: > > > Convert both callers to use the "new" errseq infrastructure. > > > > I looked at making this sort of change across the board alongside the > > original wb_err patches, but I backed off at the time. > > > > With the above patch, this function will no longer report a writeback > > error that occurs before the sample. Given that writeback can happen at > > any time, that seemed like it might be an undesirable change, and I > > didn't follow through. > > > > It is true that the existing flag-based code may miss errors too, if > > multiple tasks are test_and_clear'ing the bits, but I think the above is > > even more likely to happen, esp. under memory pressure. > > > > To do this right, we probably need to look at these callers and have > > them track a long-term errseq_t "since" value before they ever dirty the > > pages, and then continually check-and-advance vs. that. > > > > For instance, the main caller of the above function is jbd2. Would it be > > reasonable to add in a new errseq_t value to the jnode for tracking > > errors? > > Doesn't b4678df184b3 address this problem? If nobody has seen the > error, we return 0 instead of the current value of wb_err, ensuring > that somebody always sees the error. > I was originally thinking no, but now I think you're correct. We do initialize the "since" value to 0 if an error has never been seen, so that (sort of) emulates the behavior of the existing AS_EIO/AS_ENOSPC flags. It's still not quite as reliable as plumbing a "since" value through all of the callers (particularly in the case where there are multiple waiters), but maybe it's good enough here. I'll look over the rest of the set. Thanks, -- Jeff Layton <jlayton@redhat.com>
On Mon, Jan 09, 2023 at 09:31:00AM -0500, Jeff Layton wrote: > On Mon, 2023-01-09 at 14:02 +0000, Matthew Wilcox wrote: > > On Mon, Jan 09, 2023 at 08:48:49AM -0500, Jeff Layton wrote: > > > On Mon, 2023-01-09 at 05:18 +0000, Matthew Wilcox (Oracle) wrote: > > > > Convert both callers to use the "new" errseq infrastructure. > > > > > > I looked at making this sort of change across the board alongside the > > > original wb_err patches, but I backed off at the time. > > > > > > With the above patch, this function will no longer report a writeback > > > error that occurs before the sample. Given that writeback can happen at > > > any time, that seemed like it might be an undesirable change, and I > > > didn't follow through. > > > > > > It is true that the existing flag-based code may miss errors too, if > > > multiple tasks are test_and_clear'ing the bits, but I think the above is > > > even more likely to happen, esp. under memory pressure. > > > > > > To do this right, we probably need to look at these callers and have > > > them track a long-term errseq_t "since" value before they ever dirty the > > > pages, and then continually check-and-advance vs. that. > > > > > > For instance, the main caller of the above function is jbd2. Would it be > > > reasonable to add in a new errseq_t value to the jnode for tracking > > > errors? > > > > Doesn't b4678df184b3 address this problem? If nobody has seen the > > error, we return 0 instead of the current value of wb_err, ensuring > > that somebody always sees the error. > > > > I was originally thinking no, but now I think you're correct. > > We do initialize the "since" value to 0 if an error has never been seen, > so that (sort of) emulates the behavior of the existing AS_EIO/AS_ENOSPC > flags. > > It's still not quite as reliable as plumbing a "since" value through all > of the callers (particularly in the case where there are multiple > waiters), but maybe it's good enough here. I actually think we may have the opposite problem; that for some of these scenarios, we never mark the error as seen. ie we always end up calling errseq_check() and never errseq_check_and_advance(). So every time we write something, it'll remind us that we have an error.
diff --git a/mm/filemap.c b/mm/filemap.c index c4d4ace9cc70..48daedc224d9 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -355,16 +355,6 @@ int filemap_check_errors(struct address_space *mapping) } EXPORT_SYMBOL(filemap_check_errors); -static int filemap_check_and_keep_errors(struct address_space *mapping) -{ - /* Check for outstanding write errors */ - if (test_bit(AS_EIO, &mapping->flags)) - return -EIO; - if (test_bit(AS_ENOSPC, &mapping->flags)) - return -ENOSPC; - return 0; -} - /** * filemap_fdatawrite_wbc - start writeback on mapping dirty pages in range * @mapping: address space structure to write @@ -567,8 +557,10 @@ EXPORT_SYMBOL(filemap_fdatawait_range); int filemap_fdatawait_range_keep_errors(struct address_space *mapping, loff_t start_byte, loff_t end_byte) { + errseq_t since = filemap_sample_wb_err(mapping); + __filemap_fdatawait_range(mapping, start_byte, end_byte); - return filemap_check_and_keep_errors(mapping); + return filemap_check_wb_err(mapping, since); } EXPORT_SYMBOL(filemap_fdatawait_range_keep_errors); @@ -613,8 +605,10 @@ EXPORT_SYMBOL(file_fdatawait_range); */ int filemap_fdatawait_keep_errors(struct address_space *mapping) { + errseq_t since = filemap_sample_wb_err(mapping); + __filemap_fdatawait_range(mapping, 0, LLONG_MAX); - return filemap_check_and_keep_errors(mapping); + return filemap_check_wb_err(mapping, since); } EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
Convert both callers to use the "new" errseq infrastructure. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- mm/filemap.c | 18 ++++++------------ 1 file changed, 6 insertions(+), 12 deletions(-)