jbd2_journal...free_buffers(9)

📦 version 7.3.1, in nixpkgs unstable

💖 jbd2_journal_try_to_free_buffers — kernel API manual, bestie edition 💖

okay so this is a page from the Kernel API Manual, and it's about jbd2_journal_try_to_free_buffers. yes the name is long. yes it's lowkey a mouthful. no we are not skipping it. let's go 🫶

✨ NAME ✨

jbd2_journal_try_to_free_buffers — literally just trying to free page buffers. that's the whole vibe. 💅

🌸 SYNOPSIS 🌸

bool jbd2_journal_try_to_free_buffers (journal_t *journal , struct folio
*folio );

copy it exactly, don't @ me, the spacing is what it is 😭

🎀 ARGUMENTS 🎀

  • journal — the journal for the operation. it's the main character here, ngl 👑
  • folio — the Folio we're detaching data from. bye bestie, data's leaving 🌈

🦋 DESCRIPTION 🦋

okay so here's the tea. for all the buffers on this page: if they're fully written out ordered data, we move them onto BUF_CLEAN so try_to_free_buffers can reap them. slay, clean buffers, iconic behavior ✨

This function returns non-zero if we wish try_to_free_buffers to be called. we do this if the page is releasable by try_to_free_buffers. we also do it if the page has locked or dirty buffers and the caller wants us to perform sync or async writeout. multitasking queen behavior fr fr 👑

lowkey this complicates JBD locking somewhat. we aren't protected by the BKL here 🫣 we wish to remove the buffer from its committing or running transaction's ->t_datalist via __jbd2_journal_unfile_buffer.

This may change the value of transaction_t->t_datalist, so anyone who looks at t_datalist needs to lock against this function. yes literally anyone. the lock is not optional, no cap 🔒

Even worse — someone may be doing a jbd2_journal_dirty_data on this buffer. so we need to lock against that too. jbd2_journal_dirty_data will come out of the lock with the buffer dirty, which makes it ineligible for release here. it's giving ✨unavailable✨ 💀

So who else is affected by this? hmm... 🤔 really the only contender is do_get_write_access — it could be looking at the buffer while journal_try_to_free_buffer is changing its state. But that cannot happen because we never reallocate freed data as metadata while the data is part of a transaction. Yes? 🥺 (that "Yes?" is doing a lot of heavy lifting and it's in the original, so it stays, bestie 💜)

💀 return value vibe check: Return false on failure, true on success. that's it. that's the whole paragraph. periodt.

💀 SEE ALSO 💀

Kernel file ./fs/jbd2/transaction.c — and honestly the whole friend group, gathered here for you:

🎀 that's the whole page, bestie! this one lives at ./fs/jbd2, dated October 2026, and it's part of the Kernel API Manual (jbd2_journal...free_buffers(9)). go forth and free those buffers responsibly 💖✨🦋

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