On Wed, Mar 12, 2025 at 10:06:11PM +0000, John Garry wrote: > On 12/03/2025 15:46, Darrick J. Wong wrote: > > On Wed, Mar 12, 2025 at 01:35:23AM -0700, Christoph Hellwig wrote: > > > On Wed, Mar 12, 2025 at 08:27:05AM +0000, John Garry wrote: > > > > On 12/03/2025 07:24, Christoph Hellwig wrote: > > > > > On Mon, Mar 10, 2025 at 06:39:39PM +0000, John Garry wrote: > > > > > > Refactor xfs_reflink_end_cow_extent() into separate parts which process > > > > > > the CoW range and commit the transaction. > > > > > > > > > > > > This refactoring will be used in future for when it is required to commit > > > > > > a range of extents as a single transaction, similar to how it was done > > > > > > pre-commit d6f215f359637. > > > > > > > > > > Darrick pointed out that if you do more than just a tiny number > > > > > of extents per transactions you run out of log reservations very > > > > > quickly here: > > > > > > > > > > https://urldefense.com/v3/__https://lore.kernel.org/all/20240329162936.GI6390@frogsfrogsfrogs/__;!!ACWV5N9M2RV99hQ!PWLcBof1tKimKUObvCj4vOhljWjFmjtzVHLx9apcU5Rah1xZnmp_3PIq6eSwx6TdEXzMLYYyBfmZLgvj$ > > > > > > > > > > how does your scheme deal with that? > > > > > > > > > The resblks calculation in xfs_reflink_end_atomic_cow() takes care of this, > > > > right? Or does the log reservation have a hard size limit, regardless of > > > > that calculation? > > > > > > The resblks calculated there are the reserved disk blocks and have > > > nothing to do with the log reservations, which comes from the > > > tr_write field passed in. There is some kind of upper limited to it > > > obviously by the log size, although I'm not sure if we've formalized > > > that somewhere. Dave might be the right person to ask about that. > > > > The (very very rough) upper limit for how many intent items you can > > attach to a tr_write transaction is: > > > > per_extent_cost = (cui_size + rui_size + bui_size + efi_size + ili_size) > > max_blocks = tr_write::tr_logres / per_extent_cost > > > > (ili_size is the inode log item size) > > So will it be something like this: > > static size_t > xfs_compute_awu_max_extents( > struct xfs_mount *mp) > { > struct xfs_trans_res *resp = &M_RES(mp)->tr_write; > size_t logtotal = xfs_bui_log_format_sizeof(1)+ Might want to call it "per_extent_logres" since that's what it is. > xfs_cui_log_format_sizeof(1) + > xfs_efi_log_format_sizeof(1) + > xfs_rui_log_format_sizeof(1) + > sizeof(struct xfs_inode_log_format); Something like that, yeah. You should probably add xfs_log_dinode_size(ip->i_mount) to that. What you're really doing is summing the *nbytes output of the ->iop_size() call for each possible log item. For the four log intent items it's the xfs_FOO_log_format_sizeof() function like you have above. For inode items it's: *nbytes += sizeof(struct xfs_inode_log_format) + xfs_log_dinode_size(ip->i_mount); > return rounddown_pow_of_two(resp->tr_logres / logtotal); and like I said earlier, you should double logtotal to be on the safe side with a 2x safety margin: /* 100% safety margin for safety's sake */ return rounddown_pow_of_two(resp->tr_logres / (2 * per_extent_logres)); I'm curious what number you get back from this function? Hopefully it's at least a few hundred blocks. Thanks for putting that together. :) --D > } > > static inline void > xfs_compute_awu_max( > struct xfs_mount *mp, int jjcount) > { > .... > mp->m_awu_max = > min_t(unsigned int, awu_max, xfs_compute_awu_max_extents(mp)); > } > > > > > ((I would halve that for the sake of paranoia)) > > > > since you have to commit all those intent items into the first > > transaction in the chain. The difficulty we've always had is computing > > the size of an intent item in the ondisk log, since that's a (somewhat > > minor) layering violation -- it's xfs_cui_log_format_sizeof() for a CUI, > > but then there' could be overhead for the ondisk log headers themselves. > > > > Maybe we ought to formalize the computation of that since reap.c also > > has a handwavy XREAP_MAX_DEFER_CHAIN that it uses to roll the scrub > > transaction periodically... because I'd prefer we not add another > > hardcoded limit. My guess is that the software fallback can probably > > support any awu_max that a hardware wants to throw at us, but let's > > actually figure out the min(sw, hw) that we can support and cap it at > > that. > > > > --D > >
