'\" t
.\"     Title: jbd2_journal_try_to_free_buffers
.\"    Author: 
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: January 2017
.\"    Manual: The Linux Journalling API
.\"    Source: Kernel Hackers Manual 4.8.15
.\"  Language: English
.\"
.TH "JBD2_JOURNAL_TRY_TO_" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "The Linux Journalling API"
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.SH "NAME"
jbd2_journal_try_to_free_buffers \- try to free page buffers\&.
.SH "SYNOPSIS"
.HP \w'int\ jbd2_journal_try_to_free_buffers('u
.BI "int jbd2_journal_try_to_free_buffers(journal_t\ *\ " "journal" ", struct\ page\ *\ " "page" ", gfp_t\ " "gfp_mask" ");"
.SH "ARGUMENTS"
.PP
\fIjournal\fR
.RS 4
journal for operation
.RE
.PP
\fIpage\fR
.RS 4
to try and free
.RE
.PP
\fIgfp_mask\fR
.RS 4
we use the mask to detect how hard should we try to release buffers\&. If __GFP_DIRECT_RECLAIM and __GFP_FS is set, we wait for commit code to release the buffers\&.
.RE
.SH "DESCRIPTION"
.PP
.PP
For all the buffers on this page, if they are fully written out ordered data, move them onto BUF_CLEAN so
\fBtry_to_free_buffers\fR
can reap them\&.
.PP
This function returns non\-zero if we wish
\fBtry_to_free_buffers\fR
to be called\&. We do this if the page is releasable by
\fBtry_to_free_buffers\fR\&. We also do it if the page has locked or dirty buffers and the caller wants us to perform sync or async writeout\&.
.PP
This complicates JBD locking somewhat\&. We aren\*(Aqt protected by the BKL here\&. We wish to remove the buffer from its committing or running transaction\*(Aqs \->t_datalist via __jbd2_journal_unfile_buffer\&.
.PP
This may *change* the value of transaction_t\->t_datalist, so anyone who looks at t_datalist needs to lock against this function\&.
.PP
Even worse, someone may be doing a jbd2_journal_dirty_data on this buffer\&. So we need to lock against that\&.
\fBjbd2_journal_dirty_data\fR
will come out of the lock with the buffer dirty, which makes it ineligible for release here\&.
.PP
Who else is affected by this? hmm\&.\&.\&. Really the only contender is
\fBdo_get_write_access\fR
\- it could be looking at the buffer while
\fBjournal_try_to_free_buffer\fR
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?
.PP
Return 0 on failure, 1 on success
.SH "AUTHORS"
.PP
\fBRoger Gammans\fR <\&rgammans@computer-surgery.co.uk\&>
.RS 4
Author.
.RE
.PP
\fBStephen Tweedie\fR <\&sct@redhat.com\&>
.RS 4
Author.
.RE
.SH "COPYRIGHT"
.br